u/MamaMegatron

I bought a phone off of Ebay as a birthday present to myself, since I haven't had a new phone in years and my old phone's battery was giving out to the point it wouldn't stay charged for even half a day. The phone was a brand new, sealed Samsung Galaxy Note 10+ phone, that was supposed to be UNlocked. When I got it and started setting it up to my carrier (Verizon's Visible service) it wouldn't connect, saying it was locked to another carrier. So the phone came brand new, sealed, but locked to a carrier. NOT what I ordered at all!
I tried over and over to get the seller to tell me what carrier, the account, to give me an unlock code, anything, for over a week. I have even tried the major carriers I know of to see if I could unlock it myself but no such luck. I did an IMEI checker and it says it's supposedly locked to T-Mobile, so I went to a local T-Mobile store myself in person to ask nicely if they could unlock it but was told they can't without knowing the account the phone was connected to (despite the fact the phone is brand new and had never been opened until I did). When the seller wouldn't cooperate with me, I demanded to return and refund and he's been skirting around that now too for another week. I'm dealing with ebay and my bank now instead of trying to fight a losing battle with someone who's dragging out taking responsibility for what they did wrong instead of owning up to it in hopes it goes past the window of time I'm allowed to dispute it.
My problem still remains the same in the meantime- I have this new phone that I can't use while my old one is dying faster each day, because the one I bought is carrier locked due to no fault of my own.
Is there any way to unlock this phone without knowing for certain what carrier it is locked to? I don't trust these unlocking sites I keep seeing and I am not giving a bunch of money to scams as I feel I was already scammed enough. I'm not downloading any software/malware crap either. I'm not dumb, just completely over dishonest people and need a little help.
Anyone out there got any solutions that can help a gal out and let me lay the dying elder to rest in permanent retirement in the back of the junk drawer and actually use my birthday present?

Edit to add:

Model of Phone-
Samsung Galaxy Note 10+ (Model Number SM-N975U1)

I bought a phone off of Ebay as a birthday present to myself, since I haven't had a new phone in years and my old phone's battery was giving out to the point it wouldn't stay charged for even half a day. The phone was a brand new, sealed Samsung Galaxy Note 10+ phone, that was supposed to be UNlocked. When I got it and started setting it up to my carrier (Verizon's Visible service) it wouldn't connect, saying it was locked to another carrier. So the phone came brand new, sealed, but locked to a carrier.
I tried over and over to get the seller to tell me what carrier, the account, to give me an unlock code, anything, for over a week. I have even tried the major carriers I know of to see if I could unlock it myself but no such luck. I did an IMEI checker and it says it's supposedly locked to T-Mobile, so I went to a local T-Mobile store myself in person to ask if they could unlock it but was told they can't without knowing the account the phone was connected to (despite the fact the phone is brand new and had never been opened). When the seller wouldn't cooperate with me, I demanded to return and refund and he's been skirting around that now too for a week. I'm dealing with ebay and my bank now instead of trying to fight a losing battle with someone who's dragging out taking responsibility for what they did wrong instead of owning up to it in hopes it goes past the window of time I'm allow to dispute it.
My problem still remains the same in the meantime- I have this new phone that I can't use while my old one is dying faster each day, because it's carrier locked.
Is there any way to unlock this phone without knowing for certain what carrier it is locked to? I don't trust these unlocking sites I keep seeing and I am not giving a bunch of money to scams as I was already scammed enough. I'm not downloading any software malware crap either. I'm not dumb, just completely over dishonest people and need a little help.

Edit to add:

To those responding to me, please re-read my post. Maybe this will clear some things up-

I have tried official channels.
I have tried getting my money back.
The ad stated clearly it was an unlocked phone, but I got a locked phone sent to me instead. This was the seller's fault, NOT mine. I read the entire ad from top to bottom, and was anticipating receiving an unlocked, usable phone.
I never said I wanted anything for free.
I do not want to pay for downloaded software that is just money stealing malware in disguise, or obvious SCAMS. I'm willing to pay an actual tech a reasonable amount to actually unlock the phone, but not for a scammer to promise something, take my money and bail.
I realize this phone has been on the market for 7 years but it was brand new in the box, sealed in it's packaging, and not everyone out here can afford $1000+ phones every few months when they come out. Some of us can only buy something a couple years old after the ones we have finally start to kick the bucket. I picked this one because it was twice the capacity of my old one, and I'm an artist and wanted to try the stylus pen option. It's not about the age of the phone, but more about screen size, the pen function, personal preference and what I could afford.

While I know enough to get by when it comes to tech and phones, I do admit I don't know anything about the interior processing aside from what little I used to do for a living. I worked for a small company fixing broken phones, have replaced screens, casings and charge ports for a few years so I'm not entirely cell-phone-dumb and I've already researched and tried everything I possibly could think of myself already to fix this issue before reaching out to other people after exhausting the first steps of official channels and trying to return and refund.

There is ZERO reason to be rude to or curse at me. If you can't/won't help or don't have anything useful to say, then there is no need to say anything to my post at all. God forbid you ever need help with something and have to result to asking strangers for kindness in resolving your frustrating issue after you've exhausted all other options. May they give back the same energy you give.