Deducting more money for a contract than what was agreed to.

So I wanted to go from contract to pay as you go. After a phone call from Vodacom offering me a package for R79 a month, I accepted. I paid R79 for a couple of months and all of a sudden the payments increased to R141 a month!!! I logged a query and and I was told that I would be reimbursed for the extra money being paid and the account set right. This is two months later, no reimbur*****t and they still deduct R141 a month. My query number is 1- ********** ********** for I am not phoning out all of my air time waiting for 10 minutes for someone to pick up.....