Chat transcripts and accountability for incompetent support agents

Last week I noticed I wasn’t receiving the discount for also being an Xfinity mobile customer. I thought it would be a simple enough fix that chat would be an acceptable platform to get this resolved. Boy, was I sorely mistaken. Not only did my bill not get corrected, I was basically forced into a new plan which was supposed to be significantly less cost. (The new plan was also supposed to have a discount for Xfinity mobile customers).  Fast forward a week and I have received new equipment (which happens to be the exact same type of equipment that I already have.), my previous bill still hasn’t had the discount fixed, my current plan doesn’t have a discount on it. According to you the person I just spoke to, nobody can see the previous chats. How does one hold a support agent accountable for the things they said if magically nobody has access to the transcripts? Do not tell me to take a screenshot because it is not my responsibility to provide documentation of something that your company is clearly keeping records of. If there is no way for anybody to know what is said, your support agents can say anything they want to [Edited: "Inflammatory/Language"] because there’s no accountability. What is the suggested route for me to remedy this scenario?  It’s basically my word against “nobody” because I don’t even know who the person is.