Ongoing billing issue for 3 months

I have had an issue with my Xfinity Mobile bill since the beginning of June and have had multiple conversations with your team about fixing the issue on the app. On my account on the app, it currently says I owe $697.97. This is INCORRECT and I refuse to pay it. I need this to be corrected immediately. I was told that it was just an "app error" and that I didn't actually owe that money, but now every time I try to pay my bill it still says I owe that. Why is it only showing up incorrectly on my device, but apparently on Xfinity's side it looks like I have no payment due? 

This all began when I first traded in my iPhone 13 Pro for an iPhone 16e and switched to Xfinity. Then after 1 week with the iPhone 16e, I decided I meant to get the iPhone 16 pro instead. Customer service told me that would be cheaper anyway, and it was no charge for me at all. So I returned the iPhone 16e and got the iPhone 16 pro (what I currently have). Then, I was charged over $700 on June 3 with ZERO explanation. I disputed this, and talked to many representatives who all said this was Xfinity's problem and that you will fix it. Apparently it was because of a "deal" that ended since I returned the iPhone 16e, and now I owe all that money upfront? I owned the iPhone 16e for 8 DAYS.

I've spent hours on the phone with different people who assured me it was fixed. Well, months later, it's still not fixed and I don't want to have a bill saying I owe $697.97 when that is WRONG. I keep getting messages saying that I owe that, but I refuse to pay that. 

Please assist immediately, I am extremely upset and will be cancelling my Xfinity plans completely if I have to deal with this again. It's been MONTHS with zero progress. This was an extremely unfortunate switch to Xfinity mobile, and I expect credit for the amount of time and energy I've had to put into trying to fix this.