Non cancellation of Contracted

I have been trying to cancel 3 vodacom business contracts since 2014. With no success. Now vodacom has debt collectors harassing for payment on these accounts, which were supposed too be cancelled. Spoke to a consultant at the debt collectors who confirmed that upgrades have been done on the numbers. How does vodacom allow upgrades too be done by individuals on business contracts without authorisation from the company. And apparently the person who did the upgrades is a deceased employee of the company. What is going on with Vodacom, the service received is pathetic.