Return after 20 Day

I previously switched to T Mobile from Spectrum, since Spectrum was giving me the run around about unlocking my device, I ended up purchasing the device I have now which was the only phone available at the time. I absolutely hate this phone. Well I was finally able to get my previous device unlocked, however T Mobile will not take the phone back since it's out of the window. They advised to sell it and the use the money to pay off the phone but I can't get anyone to commit to 600 bucks for a IPhone 14 Plus. I'm at a loss because I'm paying for a phone that I'm not using. Any advice would be great.