Identity theft

I was a Vodacom customer for over 15 years until I ported my number to CellC approximately 2 years ago. Vodacom collected my monthly fee via debit order every month without incident. Recently I have received several calls from Vodacom claiming that I owed them money on another contract. However, I stated that I never took out the other contract. They requested that I send them an affidavit stating this along with my ID document, which I did on the 4th July 2015 (the reference I received for this email is: S3-8A819-94TM5). I did not hear anything back from Vodacom until today when I received a call from their collection agent. This is totally unacceptable, I want someone at Vodacom to resolve this issue as a matter of urgency.