Exorbitant collection charges and Overcharging on Interest

I was late with my levies and paid them in the following month and they charged me interest for the whole month when I raised it with them they told me they want to consult with the trustee first and it took them more than 2weeks to come back with a response and they charged me R777 in charges for an outstanding balance of R4k.Is there a regulation on how much these people can charge or a limit.