Fighting fire with fire
The most unethical life hack I ever heard in call centers is calling the customer from a second phone to get them to hang up on you and end the call when you can't hang up
Get an anonymous email like tutamail
Create a TextNow phone number with that email. (It's a phone app)
When you can't hang up and want to get off the phone with them they'll usually end the call or at least break their focus on you.
Place a call to the customer from your ghost number. Most people especially if they are escalated or have been given a resolution and won't hang up will take the other call and let you go.
MAKE SURE TO PUT PHONE ON MUTE!
It's good for giving them a reason to end the call.