Xfinity won’t let me pay my last bill after I cancelled my services

I cancelled my xfinity internet because I no longer require the services and I’m trying to pay my bill. Xfinity’s app which I have downloaded and fully updated will not let me pay my bill it says access not authorized. I spoke to an agent through the live chat function and I still wasn’t given a path through which I can pay my bill and told me I have to wait until 30 days after the cancellation date. I’ve been trying for three days now and the bill says “overdue” in bold red font, even though xfinity as an entity refuses to allow me to pay the bill until thirty days. If this is the case shouldn’t my bill not be labeled as “overdue” since they are the ones who will not allow me to pay under any circumstance?   I’ve been trying to somehow get my bill paid for 3 days now and I don’t know how this will affect my credit. I’m honestly deeply disturbed by how unethical and uncommunicative this process has been. And how profoundly difficult and borderline impossible xfinity has made it to receive clear communication and bare minimum  customer transparency. If you refuse to let me pay my bill even though I’ve been trying for threee days since the due date, shouldn’t you remove the past due notice? And be able to ensure to me that this will not be financially noted as a failure on my part since it is all happening on your end?