Traded in for an Upgrade and Received Several Emails Stating Incorrect Information

Hello,

I am a former sprint user. I recently traded in an iphone 11 in excellent condition for an iphone 13 pro. I was supposed to get an $800 credit over 30 months.

I used the provided mail in kit. The box started tracking immediately, while it was in transit and delivered I received emails letting me know that I needed to ship the items. I wrote that off.

I received another email this monday letting me know the phone arrived damaged and that I wont be receiving the promotional credit. I used padding and the phone was in excellent shape like I already said. 

Obviously I am upset, but the reps have told me until now that this was most likely all part of a glitch. when I checked my billing i now no longer see the promotional credit applied. 

Who do I talk to to get this resolved? What number do I call? What are my odds of being able to resolve this? 

I was dumb and took no pictures of the state of my phone prior to mailing it out, but I have the IMEI.