Billing issues

I made a payment arrangement over the phone with a Comcast associate for a specific date and amount and got an email confirmation. Come that day I made my payment and then my account had a new message the total due must be paid by today as that was now past due so I had to pay additional $291 for services to stay active. The $291 would not be a shut off past due amount until August but there telling me I made a payment arrangement for that amount. I have spent all day on the phone trying to get a resolution and no luck. I have the email and text that state my agreed payment arrangement but nobody will or can help me. Who would I speak to to send my arrangement email and get a resolution?