Overcharged on Account

After changing over from Nashua I had problems with billing on my account, due to this I changed my payments to EFT rather than direct debit. For the last few months, I have not been receiving my bill at all and since I pay on the 28th and I am only due my statement at the beginning of the month, I have been calling in to receive the amount due and paying what I am told (and in some instances, paying a little bit extra). Today my account was suspended due to me apparently owing R4900 odd! When I called in, I was told this was due to me short paying! How was I to know that I was short paying when my bill wasn't being sent through and I was being notified by Vodacom that I owed much less?! When my account breakdown was read to me I noticed that I was being charged extra for calls and data calls despite the fact that I have never run out of minutes and I have never made a data call.