Charged for unused data while sim was inactive

My review is solely on the contract. I was just left with a bitter taste in my mouth after not using both my sims in December (I was on holiday and out of the limited range rain has) yet still I was charged for the R250 Unlimited off peak, despite the fact that I did not at all use any of the sim cards in the December period, over R500 was charged. This month again I only used 1 of the 2 sim cards and still get charged R250 Unlimited off peak for both. That's another R250 I did not at all use. The sim hasn't been active at all. It does not make sense why this can be charged and I can only change it for the next month, regardless of the fact that I have not used any of the data on the 1 sim. So unreaosnable. I have searched all correspondence with rain from when I activated the sim and I still cannot find where those Ts and Cs are stated regarding being charged despite not using the data, or in my case not having the sim card active at all. What a *******!