Vodacom working with call center full of **** artists

Vodacom Must deal with these 3rd party call Center companys , Took a contract with Vodacom about 3 years ago, which i was supposed to be paying R680 but as from last year that amount started increasing but pay not much attention to it because I had other debit orders fast foward to today where I got charged R1200 and when I called I was told that There were changes made on my account by some rewards agent who I have never spoken too, so can someone please explain how does Vodacom allow these call center agents to make changes on people accounts without permission and whats even worse because of these changes it has added another year to my contract which I was supposed to be finishing in two months time but now I have to wait 14 months because of changes made on my account by these agents who are didnt get permission or Authorise from the account holder? How is our information safe if you can heir ****s artists to work at your call center for or one of your dealers? Like Rewards, which is where the agent that made changes on my account was from….. I need this address quickly and my money back for all the months I paid for changes made on my account without my authorise