Overcharged

Really I'm tired of complaining about vodacom and I hope it's for the last time. My contract was R1189 at the beginning and in November it was increased to R1240 and for the month of May I was then debited R1500. I phoned vodacom regarding this however they can't explain why the increases on my debit orders. I was promised to be called back with the answers but even today I'm still waiting.