T-Mobile and Apple Misleading Me About Trade-In Credit, Overcharging for iPhone I No Longer Own

I contacted T-Mobile and Apple before pre-ordering the iPhone 16 Pro Max because I was concerned about my phone bill becoming too expensive. During the call, I explained that my iPhone 15 Pro Max wasn't fully paid off with T-Mobile. On a 3-way call with representatives from both companies, I was assured that the $650 trade-in credit offered by Apple would fully pay off my iPhone 15. I was explicitly told that I wouldn't need to worry about my phone bill increasing beyond what I had been paying all year. Fast forward three months, and I've been in an endless back-and-forth with both T-Mobile and Apple, trying to resolve an issue that is entirely their fault. Despite returning my iPhone 15 Pro Max to Apple, I'm now being charged for financing three iPhones, even though I only have my iPhone 16 Pro Max. Every time I speak with a customer service agent, I receive false and conflicting information. Neither company is taking responsibility for the promises made during that 3-way call, and they've failed to document those conversations properly in their systems. As a loyal customer, I feel completely taken advantage of. It's unacceptable for two major companies to operate this way, especially when I've done my part to follow the process they outlined. The lack of accountability and unwillingness to resolve this issue is appalling. If I do not receive a resolution that reflects the promises made to me-including closing out the balance on my iPhone 15 Pro Max-I will have no choice but to file a lawsuit against both T-Mobile and Apple. This is not just a matter of principle; it's about holding these companies accountable for providing false information and overcharging me for a phone I no longer own. My hard-earned money is not something I will allow them to exploit, and I demand this issue be resolved immediately.