Selling defective Pre-Owned iPhones

Took an a PreOwned IPhone on contract at cellucity in September 2023, worst mistake of my life. In December the phone suddenly wanted me to update to IOs 17.2 for me to be able to be able to use mobile data (make and receive calls). Tried to update software but failed. I took it to the store on the 2nd of January to have them update the software, they failed and i had to leave the phone for them to take it to repairs. 4 days later is still don't have a phone and no one can tell me what's the way forward and yet i'm paying for the contract. Basically paying for a phone i don't have