Cell C, even when they are good they are bad.

Someone from Cell C called me a month ago to sell me a 10 Gig data bundle to add to my account, it was such a great deal I simply couldn't refuse. Somehow though they have managed to mess it up by debiting me for 2 amounts on 2 separate bank accounts one on the 1st and 1 on the 15th of the month. I tried calling in to sort out the problem and one of the security questions they ask you is which bank and day do we debit you on? How do they manage to stuff up so badly even when the are offering such great deals? This is really frustrating and I'd like someone to call me and get this sorted out.