Got a different contract from what I app**** for!!!

So I app**** for the 'Black Friday special' data deal (30GB + 20GB for R399) in November and I had to wait for a few days for approval and credit check. Within a few days, I got notification of approval and that I had to wait for somebody to contact me. I received a call in December to say that the branch I had app**** at (temporary store at Rosebank) didn't have stock so I had to pick it up in Norwood. When I was charged in January, I notice that I have been charged way more than I signed up for and it was the incorrect deal (R675 for 10GB + 10GB). How on earth does it come up to that?? Nobody at the call centre is able to assist and the temporary store at Rosebank has since closed down. If nobody gets back to me, I am going to cancel the contract!