Bogus offers from Vodacom

I've upgraded my data contract and was only supposed to pay a monthly amount of R266, which was what was billed the first month, then suddenly it's shot up to R504. When I queried this I was sent from department to department without any success. I was now billed R504 again - this is unacceptable. Vodacom is quick to warn you that all calls are recorded, but aren't willing to go back to the recording to confirm what I agreed to.