Putrid service..

So this year I decided to close my contract...I called into Mtn asked for my amount i need to pay in for early cancelation...I got it and then paid it in...called the next day to do the cancelation only to then find out MTN GAVE ME THEE INCORRECT AMOUNT I HAD TO DO A SECOND PAYMENT OBVIOUSLY EFT FROM MY PHONE NOW AS I COULDNT GO BACK TO MTN THE LADY THAT EMAILED ME THE BANKING DETAILS (FOR NOW I WOULD NOT MENTION NAME) I ASKED IF THIS IS THEE AMOUNT AND DOES IT INCLUDE MY AUGUST PAYMENT YES IT DOES (GOT THAT ON BLACK AND WHITE) PAID THEE AMOUNT IN FULL AS REQUESTED AND THEN SEPTEMBER CAME THEY DEBITED MY ACCOUNT...I WAS FURIOUS AND DID A REVERSAL I CALLED IN TO GET IT SORTED UP TILL NOW ITS STILL NOT SORTED...I GOT AN EMAIL SAYING THEY GOING TO BLACKLIST ME WHICH IS SO FRUSTRATING AS THEY WERE THE ONES THAT GAVE ME THE INCORRECT AMOUNT NOT ONCE BUT TWICE AND EVEN WHEN I CALL IN TO SPEAK TO SUPERVISOR THEY ALWAYS IN A FLIPPEN MEETING.THEY GO ON WITH THEIR LIVES AND IM HERE TRYING TO AVOID BEING BLACKLISTED FOR THEIR STUPIDITY...I HAVE BEEN CALLING IN NUMEROUS OF TIMES AND ALL THEY CAN SAY THEU LOGGED THE CALL FOR A CREDIT AND I HAVE BEEN HEARING THIS SINCE SEPTEMBER WE IN NOVEMBER AND STILL NOTHING....I THINK ITS TIME I TAKE THEM TO COURT FOR WANTING TO BRING MY NAME DOWN THE GUTTERS...UP TILL TODAY NOW RETURN CALLS NOTHING