In Quicken unlink the bill and just record a scheduled reminder which does not execute as an online payment into your account register on or before the Due Date and before you download transactions from the bank or credit card containing the payment transaction. That will allow Quicken to match your register transaction to the downloaded data and not cause any further issues.
If you haven't done so already, I'd say it's time to call Quicken Support on the phone during posted hours of operation and request help. Let them do a screen share session with you to review the situation on your computer, to determine the nature of the problem and to figure out how to fix it.
Quicken Support: