How to resolve shortfalls re: terms firmly offered and accepted for Xfinity Mobile?

This is a long story even in shortened form, but I hope someone may have some kind advice about how to go about resolving a huge gap between two aspects of (1) the terms that Comcast firmly offered and we accepted for Xfinity Mobile last fall, and (2) what actually has been the case so far in regard to device trade-in values and free lines, with significant shortfalls in both of those areas. If you're interested, please read on.

On 10/3/2025, a Comcast employee (I'm leaving out all personally identifying information here in public) in the home internet retention office persuaded us to move to Xfinity Mobile with a firm offer of $1,100 device trade-in value for each of our 2 iPhones, with no contingencies (or language of "up to," etc.), and 1 year of free Premium Unlimited service for each of 2 lines, since we have residential internet service accounts at 2 locations. All of this, including reconfirmation of those firmly offered terms, is documented in my contemporaneous notes from that call, and must be clearly documented in Comcast's recording/transcript of that call.

However, we only received $700 per device trade-in (total shortfall there of $800!) and are being charged $40/month for 1 of the 2 lines that were offered and accepted as "free" for 1 year. So far, the incorrect monthly overcharges have accrued to well over $200 and counting, with the eventual prospect of a $1,280 net shortfall relative to the terms that were offered and accepted. After four months and tens of hours of wasted time with generally well-intentioned CS reps, including Tier 3 support and a "value add escalation" ticket, none have been able to resolve this, only to sympathize and refer it on to other offices. This has been an astoundingly frustrating customer experience.

Most recently, that process has become a loop. Due to a seemingly misdirected internal ticket that languished for more than 2 months of what must have only been said to be work to resolve it, we were finally advised that it had landed in the wrong department 2 months earlier, and that we should start over by calling the general CS phone support line. Having started months ago with general Customer Service and learned from them that they understood the issue but would need to escalate the matter, this would seem worse than futile to repeat.

Because the individual reps I've dealt with (aside from the latest stunning moment of the ticket wasting away for 2 months) have understood the problem and done their best to escalate it for resolution, I would love to avoid having to start a formal dispute (arbitration?) process for this clear breach of two key terms that were offered and accepted; but I'm seemingly out of other options, aside from sending up a distress flare here or jumping onto social media to complain, which I would love to avoid.

If anyone knows of a way to get this type of glitch directly to a Comcast department that has the power to actually fix it, I'd be immensely grateful to learn of somewhere I could send thorough documentation of the issue's foundation and its history, without having to explain it all in real time in a long phone call with front-line Customer Service. Many thanks in advance for any leads!