Cancelled Internet Service But Still Being Billed

After reading several other posts, this seems like a common problem, but I am still being billed for services cancelled on 21 May 2026. I have chatted with at least 3 live agents who all confirmed the account was cancelled, but when I login, it shows upcoming bills and amounts past due. How do I get Xfinity to end the service and remove the amounts incorrectly billed? I have called, chatted, and submitted a trouble ticket, but the issue persists.