Billing Charges

I am trying to sort out a billing problem on my account, I have not recieved a statement for the past year or so, I contact Vodacom and they say they will sort it out, a few months later I contact them as I still have not recieved a statement and this carried on until now, still not recieving a statement! I later do research into the contract they migrated me to and I find I am paying more than what I should be(as stated by one of their sales managers)I contact Vodacom, they say they will get back to me and after a month, still nothing! What does a person have to do to get some sort of response from Vodacom? On top of all of this I cant even Log Into my account on their website to view my statements because there is always an issue with their online services!!!