Vodacom billing

I am a vodacom customer from the day cell phones came out. Same number all the years and never changed my number nor skipped a payment. February i received an account of R 10 800.00 Data use. You can never use that type of data in a month. I queried it and after a long fight and was send from pillar to post they came back to me saying they see there was a problem and will give me half discount. Why know i asked because if i paid they would not come back and say sorry you paid too much. I said that still cannot be and go back and investigate more. Till today they never came back to me. Yesterday i received a invoice for R 33 000.00. Trying again to resolve the problem but no one can give me an answer. My question is how can you still bill me if my number does not WORK any more. my line is closed and i don't use there service. HOW CAN YOU BILL ME???