Xfinity did not honor flagship Samsung promotion of $300 off New S23 Ultra

Hi! I've been eyeing on the new S23 ultra since it first came out and I've compared different stores and website to find the best deal, and in the beginning of August 2023, they have a $300 off promotion on the new Samsung S23 ultra. I tried getting the new phone online but for some reason I cannot find my device in my account so I go to the store that same week, however the agent was unable to help me as well. The mobile expert at the store was able to open a ticket to help resolve this issue within 7-10 days. Come 2 weeks later, heard nothing from xfinity. I come back to the store to find a solution, they recommended I open a new line which I paid $105 plus the first payment of the phone which was $50 (full price). I ask the agent if I don't need this new line, can I get a refund? To which he said yes. Ok, 3-5 days later, I get my new phone, switched it to my old number, works just fine. But Xfinity is still billing me $49.99 (full price) on the phone. I keep reaching out to the store, online, and customer service, they all start a ticket but nothing is ever done. Xfinity never called me back! So now it's October, I come back to the store with the agent who recommended I open a new line to get the promotion, I wait almost 2 hrs while he talks to 3 different agent on the phone from xfinity, only to tell me that the best he could do was a $50 credit. They gave me a bunch of different excuses like, "the promotion was only good for 4 days", "because she didn't avail the insurance", "because I opened a new line". That does not make sense!

Wtf am I supposed to do now?