Billing issue

Hello, My bill in my Xfinity account was saying one amount which I was paying for my internet that an agent confirmed with me in an online chat and then a couple days later my account went up an extreme amount. I don't understand why customer services would have me send documentation showing proof of what agents tell you in transcripts and a bill showing proof when they are not going to honor it. The agents online tell you one thing , the bill can change at any time and then they make me seem like I am not understanding things. I have been with Xfinity 13 years. This is the first time I have had to post on a forum to try and get help.  Xfinity should be asking me what they can do to help me fix my bill but instead I feel like they get me all confused. Why is it that it just can't be a simple fix. Instead I was on the phone with customer service 10 hours one day, been online chat for several weeks over and over , talked to customer support and I feel this is still not resolved and in the meantime I could get my internet suspend all because of their extreme confusing billing issues and their customer support for their customers