High billing and no straight answer

Very bad experience and high billing with no straight answer I recently took a contract with telkom last year December and my bill was always high until recently I went to the shop only to find that my spend limit was set on 500 now what makes things worse was that last month it was rectified and my account was debited an amount of 1836 now the bill just came through which says I owe an amount of 2747 they have added the 1836 which I cearlry don't understand why I have had it with telkom the service I'm getting is really bad and I would like this matter to be rectified