TOTALLY OVER CHARGED ME

I HAVE A VODACOM CONTRACT FOR 2 MONTHS TOP UP CONTRACT OF R199PM ON THE 02/11/15 A DEBIT ORDER OF R3715.76 WAS DEDUCTED CALLED MANY TIMES 2 QAURY THIS AND AS USAUL THEY PUT U THRU DIFRENT DEPARTMENTS THEN THEY SAY ITS A OPEN LINE HOW DA HELL CAN A TOP UP CONTRACT ALL OF A SUDDEN G2 A OPEN LINE .... NOW THANX 2 VODACOM THEY PUT MY ACCOUNT IN A MINUS