Deducting money unnecessarily

I have a existing account with Telokm @ Longbeach Mall., for almost 1 year with them and never had a problem, but yesterday i saw on my bank statments that there was R 912.00 deducted (Nudebt Telko***G150523) is the reference used, i called the number on my statement ***) they informed me that i was apparently owing Telkom money??? They are deducting EVERY single month how is this possible? I need either a call back explaining this and refunding me before the end of the day please