Xfinity not honoring chat offer - So frustrating!

My current promo deal for the internet just expired. I reached out to customer service couple of months ago and I was given a new deal that would kick in right once the old one expires. Well, I was lied to since my current bill is double the amount and there is no loyalty discount anywhere. I reached out to customer service this morning and they cannot find any record of that chat or promo being applied. I have whole chat saved, along with the confirmation number, but they are saying there is nothing they can do to honor the deal since it is not showing on their end. On top of everything, they told me there is no deals available right now for my account and that I will just have to accept the new bill, because is the best price i can get. Really beyond frustration. Xfinity recognize me a diamond member, but they for sure are not treating me like one, by laying and providing bogus promos/loyalty discounts. I would really like this to be looked at closer, and the promo be honored as promised.