Data Dispute

I had a problem with Telkom my contract I am paying 139 for data 10GB and suddenly I had a shocked bill to say I owe telkom R2016 which I don't know anything about and wen I call and dispute that they tell me it's out of bundle and how I don't know cause I set my spending limit to zero and also make it not to redirect after finishing up my Data now I have to pay for data that I hasn't use but with this experience I am going to cancel my contract with them, I cannot pay for data much for Data