Help with account issues - already spent HOURS with Cus Service

I am caught in an infinite loop when I try to pay my bill - to add a payment type. Error message saying that they can't verify my account, to add email or cell number WHICH DISPLAYS when linked back to contact information on site!! I think it's an issue with a new cell number which is by another account user. And also, the phone that was originally assigned to the xfinity account is NOT a mobile, so doesn't match the cell phone number now entered. But trying to explain this to customer service just leads to tears (mine!) and the same conversation over and over. Last discussion - after an hour + they transferred me to billing! And I got promptly disconnected. I've been a customer for over 25 years. This is disgraceful. Any advice? Thanks.