Overcharged for a contract

I'm not happy with the service I received from this service provider. I took a contract with them on a promo they had for 80GB data with a pocket router for R336 a month in first week of June. They first gave me a sim card with 30GB when I query it they told me to bring it back they made a mistake. Promised to cancel it and register the correct sim which I did two days after. To my surprise they where suppose to debut on the 25th of June but they debited R358 on the 8th of June and again on the 25th of June they debited R795. Tried to call Vodacom Mall of America they told me they don't do payment I have to call account center which I did. Logged a call they promised to get back to me cause they don't know what happened. After two weeks I managed to get through to them again following up and I was told to go back to Vodacom mall of Africa and tell them to call them. I gave them the shop contact number to call them and sort it out so that I can get my money back but no one ever got back to me or get my refund. I'm still worried how much this month will be debited from my account cause since I gave Vodacom my bank details they just debit any amount they want anytime. Please can someone hear me, I want my money pls.