Trade in credit not applied.

We traded an iPhone 15 plus in on October 22 of last year and still haven’t received the credit the credit was for the line *************. We turned it into the store at broadmoor in Colorado Springs. The representative Caleb took the phone and said he would apply the credit. The manager Alex knows that the phone was received and won’t give the credit. I don’t know what to do as the credit never showed up on the account and I had talked to the chat 35+ times and called 40+ times.  It’s been over 3 months. We need the credit for the phone that the store lost.