Incorrect information given to customer

I called head office asking them how much fees outstanding do i owe to them..their response was R3635..After me paying the full balance to them,they call me a month after telling me that i still owe them R3900!!!..What i dont understand is that why didnt they inform me the correct amount at first...This is not acceptable and its poor customer service..they are the wost consumers to ever do business with they are not professional..i got this information regarding the outstanding amount from Akhona Madwentshu team leader Tumelo...i spoke to many people they need to look up on they system how many times i have called and listen to they records...i want action to be taken against them immediately.....i wouldn't advice anyone to do business with them