MTN CONTRACT INCORRECT BILLING NOT BEING SORTED OUT

I NEED FEEDBACK AND THIS ENQUIRY SORTED OUT TODAY. I TOOK OUT A NEW CONTRACT WITH MTN IN JUNE, CONTRACT VALUE WAS R689 PER MONTH. FIRST MONTH I WAS BILLED R1160 WHICH THEY SAID WAS PRORATA FOR JUNE AND JULY, JULY I GET AN IVOICE AGAIN FOR OVER R1000. THE AGENT AT THE BRANCH IN FARRARMERE HAS BEEN LOGGING QUERIES FOR A MONTH NOW AND AGAIN I AM BEING BILLED ALMOST DOUBLE WHAT THE CONTRACT VALUE IS I SIGNED FOR. SORT THIS OUT PLEASE. I AM NOT EVEN USING THE SIM CARD SO THEY CANNOT SAY IT IS EXTRA USAGE. SORT THIS OUT.