Telkom charged me for unknown calls...is this not *****ing?

I received my bill from Telkom and I have an additional charge of R499.72 to my bill for calls made from my Tablet . I normally don't make calls from my tablet, I currently don't even use my tablet since I have my cellphone and I live in an area where the network coverage is really poor, but now I am liable for calls I did not make that bring up a bill this high. I am extremely concerned about this because when I checked my device, no phone calls were made from it. Telkom would not even assist in finding out who these numbers belong to, even after I reiterated that I cannot identify these numbers and I most cetainly did not make those phone calls. I have a few contracts with Telkom and basically I run the risk of having money being ****** from me every month. The call center was extremely unhelpful because they just tell me the matter will be escalated and looked into, then they come back and tell me that I still need to pay the money. I was on hold for more than 30 minutes waiting for some assistance. I think it is really unfair that Telkom can ***** money from us like this and there is no assistance from Telkom to investigate how this happened, meaning it can happen until the contract expires...Telkom can keep taking my money...and nothing can be done about it