Over billed

In november 2014, I upgraded my contract which was a top up and added another phone on the same top up account. A week later I discovered that, one phone was on top up and one on open line, I went back to Alberton branch to complain. They said my money will be refunded which I am still waiting for, and again beginning of this month they tried to debit R 1700 from my account, Whereas they were only supposed to debit R 120. I feel that Vodacom has failed me because they keep on deducting my money for their mistake and also fail to refund me.