HARASSMENT AND WRONG BILLING

I FEEL I AM BEING HARASSED BY MTN FOR A LOUSY R65,57 THAT I PAID ALREADY YESTERDAY. I've been trying to get a resolution to my queries. Does MTN take their customers seriously or not?I have paid BEEN BILLED WRONGLY I UPGRADED MY CONTRACT ON THE 02 MARCH 2019 AND I SIGNED THE CONTRACT MY MONTHLY PAYMENT SUPPOSED TO BE R666 I HOWEVER OWED THEM R31 some cents for airtime and the outstanding R65,57 WHEN I CALCULATE MY BILL SUPPOSED TO BE R716.00 EXCLUDING THE R65,57 THAT WAS DUE WHEN I CALLED TO QUERY THIS MATTER I WAS INFORMED THAT ITS THE VAT THAT IS LEADING IT TO R748 SOMETHING OFF WHICH I FAIL TO UNDERSTAND EVEN THE CONSULTANT THAT WAS TRYING TO EXPLAIN IT TO ME DIDN'T REALLY UNDERSTOOD WHAT SHE WAS SAYING,CAN I GET SOMEONE TO EXPLAIN TO ME MY CONCERN WITH REGARDS TO MY BILL. I CANNOT ALLOW THEM TO OVERCHARGE ME IF THEY CAN HARASS ME FOR A LOUSY R65,57 AFTER MANY YEARS OF BEING A RELIABLE CUSTOMER. IS THIS THE WAY OF CHASING CUSTOMERS AWAY?