Poor service by contract cancelation department

Vodacom continues to bill me after I asked them to cancel the upgrade contract as their salesperson **** to me about the contract package and duration. They send a courier to collect the handset device early in January but they are still charging me for a device that is in their position. They did a credit on my account and the next thing they are billing me again. I'm tired of calling them day by day, week by week, month to month just for them to do their work. I want Vodacom to explain as to what is difficult for them to do the right thing. I was reconsidering taking a contract with them in the near future but I'm thinking of going to either Mtn or Telkom.