HIGH BILLING ON MY AIRTIME

I AM SUBSCRIBED TO INTERNATIONAL CALLING PLUS WERE VODACOM DEDUCTS A MONTHLY ZAR5.00 FOR THIS SUBSCRIPTION WHICH ALLOWS ME TO MAKE INTERNATIONAL CALLS USING FAVOURABLE RATES ON 3RD OCTOBER I AMED A CALL TO ZAMBIA AT 8:50 PM AND IT CUT. I RECHARGED FOR ZAR 100 AND CALLED MY MUM AT 8:55 PM AND THE CALL CUT AT 9:07 PM BECAUSE THE ZAR 100 FINISHED IN THAT DURATION. I HAD NOTICED A COUPLE OF DAYS EARLIER THAT MY AIRTIME WAS GOING FAST BUT DIDNT PAY MUCH ATTENTION UNTIL THIS INCIDENCE HAPPENED. I PUT ZAR110 RAND ON THE 1ST OCTOBER, ZAR 55 ON THE SECOND AND ZAR 100 ON THE 3RD AND ALL THIS AIRTIME WAS CHARGED AT A HIGH RATE FOR MY CALLS TO ZAMBIA. JUST FOR THE ZAR100 FROM 8:55 TILL 9:07 I WAS BEING CHARGED ABOUT ZAR10 PER MINUTES WHICH ISN'T EVEN THE NORMAL CHARGE! I CALLED VODACOM IMMEDIATELY AND SEVERAL TIMES THERE AFTER BECAUSE THEY WERE NOT GIVING FEEDBACK. I ESCALATED TO THE SUPERVISOR LUCAS MAPONYA AND IT'S NOW 10 DAYS NOTHING RESOLVED. THE LAST SMS I GOT IS THAT THE CASE WAS BEING INVESTIGATED BY CIS FROM THEMBA AND KEKETSO. TODAY I PHONE AGAIN AND AM TOLD THE CASE IS CLOSED. I FEEL CHEATED AND FRUSTRATED AND AM A LONG STANDING VODACOM CUSTOMER. ALL I NEED IS ANSWERS. PLEASE REVERT