Over charge on my account

I took a 2GB data bundle contract from MTN on 22-05-2015 for the cost of R119. When I received my bill it was for an amount of R1140. I can't understand how my account could have reached so much. According to my understanding and budget I was only going to pay R119 per month for the contract. I have tried numerous times to contact MTN customer services but can never get through to them. I have also gone to the MTN shop at Galleria Mall in Amanzimtoti but they always tell me that MTN is on strike and they can't do anything about it. So how do I get back the money that they have deducted from my account. Please help