Raise defence of prescribed debt

I have never received an sms, a letter of demand or any phone calls from Capitec bank over the past 4/5 years. First of all in all legality, my agreement was never with DMC in the first place, but with Capitec.This loan was sold off to DMC. Out of nowhere this guy rocks up and said that he is collecting on an outstanding Capitec Loan, on behalf of DMC & that I need to make payment or choose the easy payment options.The documents he had in his possession was dated \24/08/2015".Only upon request for these documents"