Incorrect billing due to incorrect contract

I was contacted by a Mark person from Cell C direct during December 2014 and a was sold a R99 Top Up Data contract. I then received the contract sim card and then commenced using it. After a while I noticed that when I do a balance enquiry it shows an amount due of R146.00. I then phoned the cell customer service devision and the lady confirmed that this was a preportional amount due to the contract being taken out at a certain time in the month. My bank account was then debited with the above amount. After a few more weeks I again checked the balance on the data sim card and it then showed an outstanding balance of R265.00, I again phoned cell c direct and was advised that Mark opened an open line contract for me instead of an top up data contract, he then phoned me and advised that this will be sorted out and a new sim card will be sent to me and I was advised that i would not be debited for the incorrect contract balance. I received a new sim card. On the 16/02/2015 my bank account was debited with R342.00 and R99.00 by Cell C and I'm now getting the run around from them about refunding this amount as i never requested and open line contract.