REgardless of whether the debt collector actions are covered under the FDCPA, if the debt is paid, there is no debt upon which any debt collector may continue collection activities. 

While civil action might not be based on the FDCPA if not considered personal, which in this case it arguable could be, their would still be civil remedy under state law governing a business attempting to collect on a non-existent debt.  Its just a venue issue.