I never had an account with them

Early this year I received a call from an Markham agent informing me that I owe them and my account has been in errors for months now told the agent I had no account with them they advised that I send an affidavit confirming that I did, few weeks later I received a call from their lawyers being advised that my matter was handed over to them and I had to pay within 10 days otherwise I will be taken to court I rep**** told them I knew nothing about the account in errors I was told again to send another affidavit and they will investigate until today am not even sure if they haven't blacklisted me as yet and its unprofessional of them to be quiet after I have sent all the required docs what a service shame on you guys , will never advises anyone to be associated with such unprofessional people