Xfinity won’t let me pay final bill

I canceled my services on 6/23-6/24 . I have final bill due . I am unable to pay online nor over the phone because I am not a customer . I have filed a fcc complaint but still trying to resolve this issue asap . How do I pay my final bill as a former customer? This is insane. Crazy how Xfinity makes it hard for former customers to pay their bill. I’m so happy I left the service. I don’t recommend Xfinity no anyone . To much issues with Xfinity this past year, going down hill. Smh