Xfinity payment processed yet we have a late fee.

My father paid for Internet services a few days prior to the billing due date. The payment was fully authorized and processed and was sent to Xfinity. However, we were contacted that our payment was overdue and never went through. My dad has NEVER been late on a payment and hasn't changed how he's done it. How is it that now suddenly it's not going through. I contacted customer support for billing services and it was genuinely like talking to a brick wall. When trying to get in contact with a supervisor within the department I got hung up on. I have never had such abysmal customer service and looking through bank statements to confirm our payment DID go through. So what's the deal Comcast? Where did our money go? We will be looking to a new service if you don't take care of this situation because this is genuinely ridiculous.