Contract fees for deleted number??

I have not had a contract with Vodacom for over 6 years. I paid up my contract and received NIL statement before I moved to MTN. In fact they deleted my number from their system and when I wanted to continue using my same number I was told its deleted and I need to get a new number. Now after all this time I am being phoned by MBD attorneys and told I owe Vodacom money. Prescribed debt if any. Do me a favour loose my new number or face harassment consequences!!!!! If YOU deleted my number off your system how can you still charge me for contracts if the number dont exist!!!