Promotional Trade-In Credit Never Applied to Account?

Back in April 2022, Sprint had an offer for a Pixel 6 for free after trade-in (original value $600). A customer rep online gave me that offer and said it applied to my Pixel 5. Of course, I was aware that I had to pay the tax on the phone and the activation fee, totaling nearly $80. But Sprint/T-Mobile started charging me for the phone $25 per month for 24 months with only a $12.50 credit, basically charging me $300 for the "free" phone. I called and they claimed that my phone was a Pixel 4a and only qualifies for the half price promo. I had to send photos and screenshots of my phone as proof. They then gave me credit for the overcharge and assured me that I would be credited properly after that. Of course, they were wrong and I have to call back every month or 2 to get my credit. Luckily I have the email transcript of the original offer with the details, but even once they denied the refund. I called the following month and was able to get the refund. I'm now calling every 2-3 months, because it takes so much time to get this resolved. It really isn't worth my time and frustration for $25 each month. I HATE SPRINT/T-MOBILE!!!!! If I didn't have a contract with multiple phones to pay off I would drop them in a heartbeat for this BS! I don't think they are screw ups, I think corporate doesn't want to fix these issues because they figure that the customers will give up and that's a lot of extra cash for T-mobile. At this point, when people ask me about my service, I tell them to go to Verizon.