Eskom *****ing money from customers via penalties on prepaid electricity

So this morning I bought R150 worth of electricity units via my Capitec Bank app - the result came back with only R60 being app**** to units (of which I only received 58.03) and a R90 penalty? I am prepaid - what the hell was the penalty for? I buy units every month, and never ever have I run into a penalty for prepaid. Is this a new way of *****ing money from your customers????