Helpless Vodacom customer

I took out a new contract for a router in May 2016 at Vodacom Fourways Mall. The person who assisted me (Mabel Kunene) for some reason did not register the contract correctly and I did not receive the data for which I was paying for a couple of months. In May this year, believing the contract was up, I tried to cancel it but was told that because of Mabel's inefficiency the contract continues until August i.e. I am being forced to pay for 3 additional months! I have been back to the store and have appealed to Alistair, the store manager, I have phoned the help line and the legal department, but to no avail. No one comes back to me and no one is prepared to help. And believe it or not, Mabel still works at the Fourways Mall store!