INCORRECT OVER CHARGES!!

I am writing this review as I am highly disappointed with Telkom, THE STATEMENT I GOT IN MARCH AND NOW APRIL IS DISTURBING. I have a sim only data with them currently since I finished my phone contract last year of which I am supposed to pay R159 MONTHLY which I am doing without fail. I always pay extra monthly I am surprised to get a statement saying this month I should pay R467,90. I WANT THIS RECTIFIED AS I HAVE A MINUS BALANCE, YOU GUYS ACTUALLY OWE ME OR CANCEL MY CONTRACT KLAAR.