Infuriated client who is not able to use their benefits!!!

I'm so frustrated and infuriated! I setup an instruction on my phone to forward calls when I am unreachable! So that happens... Whenever I try making calls from my Cell C number(the one I forwarded) I am unable to do so because I always have insufficient funds. So I ask myself how??? Called them (Cell C) to cancel the contract because I wasn't able to use the benefits I am paying for! In the process, I found out that my minutes have been depleting because of the forwarded calls, like HOW??? So when I receive a call, the caller pays and so do I??? What is that? Now my question here is this... why was I not notified that I will incur a charge if I forward my calls??? I mean I might be paying a small amount, but imagine if R800+ of my money was being lost like this???