Monthly billing support

Hello! My name is edited:[PII] and I have a question on my most recent bill. Back at the end of December, I was charged $66 for my internet bill which was an increase in price (with no warning) from my previous monthly payment of $45. I messaged with Xfinity at the end of December and they assured me that my bill from Dec -Jan would be back to the $46 a month, with no change to internet speed, and a promotional offer. They even granted me a $20 credit for this mistake. However, when I was charged for this month, it was back to $66 (minus $20 so 46, but should have been $26 if Xfinity did what they promised of continuing my contract of $46 a month. With that being said, I am asking for a refund of an additional $20 for this months extra charge and a signed and written contract that my monthly cost will be $46. I don’t want a verbal commitment but rather a written proof that your customer service will do as they say, and will charge me the $46 from here on out (and not just say that to get me off the chatting system, when in reality your customer support team knows I will be charged $66 as that happened last time). Thanks!