Ridiculous interest

Telkom seems to be one of the biggest ****s thus far. I have a contract with Telkom, I pay R99 every month for data. I once missed a payment I didn't have money on my account on the agreed date and for a missed payment of R99 they charged double interest which amounted to R300 that I now have to pay back. That interest is ridiculous if you ask me and what frustrated me is that non of that information was explained when I agreed to take the contract. This is ****************.