Incorrect billing - Paying for services not signed up for

I had taken out an open line Vodacom contract in June 2017. My contract monthly amount was supposed to be about R429.00. I am now being debited over R2000.00 per month. I have been purchasing data off my contract which I am fully liable to pay for and I have a total of this amount on my invoice. I am certainly not liable to pay for data that is used for Opera Telkom Services which was automatically added to my bill without my knowledge and consent. I would also like to know why this is not explained at the start of the contract. Cancelling this service does not work either. I expect to receive a full refund for the additional amounts debited in respect of these services for the months of July 2017, August 2017 and September 2017.