Essentially being forced to sign a resignation letter
(I am on the F2 visa)
Hello! I am hoping that someone could give me some insight into this. After I handed in my resignation letters (both in English and Korean), my boss said to me on the following day that I need to sign and fill in a company made registration form. She showed me the ones with the old format, saying that all Korean teachers have signed it before they left. She then said that there would be one with a new format, show it to me briefly (it was all in Korean) and stated that I could take a picture of it after I was done signing it. Of course, I did not sign it.
Anyway, my questions are, if my resignation was accepted, is it legal for them to make me sign it? Do I have to sign it? Is there any hard proof that I can show her to prove that I don't have to sign it?