Xfinity is not honoring my mobile trade in and closes my case exactly 21 days after it get open. 3 times in a row!

I got a new iPhone 15 in end of September and traded in my iPhone 11 for a $700 rebate in the course of 24 months in the form of monthly bill credits. Sent my phone to Assurant and got back my phone after 2 weeks with a rejection reason "LCD Damage". There was no damage what-so-ever to my phone and screen and this looks like a clerical error so I contacted Xfinity support and they open a case (Case#1) for me. They told me that someone will look into the case and get back to me. Exactly after 21 days I got an email that my case is resolved and closed and that I should receive an email about the same. I never received any email regarding that! I contacted Xfinity again and they apologized for the same and open another case (Case#2). They said that I need to send me phone back and I should receive an email with instructions and shipping label. Never Received! I called back and they asked me to reach out to Assurant directly and gave their number. Assurant phone line never let me pass through the automated phone line though I tried several options. I call Xfinity back and they apologized again and told me that they escalated my case. Right 21 days after my case#2 was opened, I got an email that my case is resolved and closed and I should receive an email. Never Happened!! I called back and Xfinity support suggested that I should go to my local Xfinity store and show them the phone. I went there with my phone and the lady at the store helped me open another case (Case#3). She checked my phone thoroughly, talked to Xfinity Phone Support for 30 minutes and took images and video of my iPhone 11 and attached to the case. Phew... all seemed good.

I called after a few days and Xfinity support told me that my case should be resolved soon. As for past 4 months I was paying higher amount so the rep credited $116 back to my account and told me "Don't worry! your money will not go anywhere and sorry for the long wait and inconvenience!". Three weeks after that date, yesterday I got an email that my case has been resolved and closed and I should receive an email about the same. Never happened!!! Moreover I got my new bill with $116 credit reversal. I called in Xfinity support last evening and was told that the credit was given by mistake and case is closed so nothing can be done!!!! I asked the rep if there is somebody that I can reach out to or what should I do other than opening another case (Case#4)

FOUR months, THREE cases (ECM0004667956, ECM0005373223, and ECM0005976070), at least 15 hours time spent (wasted). NO RESULT!!!!

What the heck!!!! Is there such thing within Xfinity as "Customer Support"?

I am feeling ripped-off, cheated and exhausted. Luckily I have my personal call logs and all the transcripts. I must have spent over 15 hours talking to support via online or phone.

I would appreciate any help here!