Penalties for changing service

I have Telkom LTE. A mission to get, but managed. I've been trying to downgrade from a 30GB pm to 20GB pm. I have a monthly contract (no long tied in contract period). I only pay for the LTE service, not for the router. I've been told I would be charged a penalty fee of R800 to downgrade to 20GB. This is absurd as the difference in price between 30GB and 20GB is only R100pm. The consultant also can't tell me how this R800 is calculated (dangerous lack of transparency - against CPA) I don't understand why i should be penalised, it would be a different story if i had a lengthy contract, but i don't. This kind of penalty is surely against what the CPA stands for and is surely designed to prevent downgrades, however I as a customer have the right to choose which product i'd like and shouldn't be penalised if Telkom is not negatively affected by this. It is not as though Telkom have accounted for me as a debtor from which they plan on receiving \x\" pm, this is exactly why i chose not to enter a termed contract. If i don't have the flexibility to change, then i might as well have taken a termed contract. "