$1,100 iPhone 13 Pro Max trade-in credit never applied — case reopened twice, still unresolved after a year

I am posting here because chat and phone support have not resolved this in over a year, and I am hoping a moderator can escalate it.

Timeline:
- Sep 25, 2025: I traded in my iPhone 13 Pro Max 1000GB. Transaction [Edited: "Personal Information"] was accepted by Xfinity on Oct 28, 2025. I was promised a $1,100 trade-in credit.
- A duplicate transaction for the same phone/IMEI, [Edited: "Personal Information"], was cancelled by Xfinity. My case later noted the previous ticket was invalid due to an upgrade error on Xfinity's side.
- Since then I have been charged the full device fee every month. The $1,100 credit has never appeared.
- Late Sep 2026: phone support promised a refund of over $500 and a corrected device charge of about $15/month, saying the credit team would reply within 8 days. Nothing came.
- Oct 9, 2026: chat support said the credit would apply to the Sep 17–Oct 16 cycle and show on my Nov 6 autopay. On Nov 6 I was charged $145.10 — the same as my Oct 29 bill. No credit.
- Oct 16, 2026: an agent opened an escalation and referred me to Assurant (1-855-884-9771). No case number or date was given.
- Oct 26, 2026: an agent offered a mobile-care callback. It never came.
- Oct 29, 2026: case [Edited: "Personal Information"] was created, with a senior-team review promised in 24–48 hours and a closing date of Nov 5. It closed on Nov 5 with no answer.
- Nov 8, 2026 (today): chat support told me the credit was denied because the trade was not completed within 21 days. I dispute this — the trade-in was accepted by Xfinity. The agent then suggested I visit a local office; I already did, and the store said they do not handle this. After I pushed back, the agent apologized, said the case was reopened with notes sent to the investigating team, and promised a resolution within 7–10 days — but gave no new ticket number.

What I am asking for:
1. Apply the $1,100 trade-in credit.
2. Confirm the refund amount and date.
3. Correct the monthly device charge.
4. A written answer, not another ticket that closes without a resolution.

Thank you to any moderator who can help escalate this to the team that can actually apply the credit.