account debit for more than my debit amount

for the month of April my account was debited for R1227.00 for what I am not aware of as my account is up to date and not in arrears, I have tried calling MTN the entire day today the 04/05/2015 on the customer care number from my cell phone 808 and when I select to speak to a consultant I get cut off, I sent an e-mail for someone to contact me and received an e-mail saying someone will contact me within 5 business days, I have now tried again and I am holding on for the last 18 minutes and counting. this is totally ridiculous as they were not authorised to debit my account for so much and now I am sitting on a minus with the bank and other debits have not gone off, who is going to be liable for these unpaid debts and for bank charges. I am an extremely furious customer and I urgently need answers as to what is going on, please can someone help. if MTN is experiencing high volumes of calls it either they have too many issues and have over promised and cannot deliver or the staff they have is inexperienced and insufficient. MTN are ******* as they have ****** my money and they need to be exposed. I have finished timing my complaint and I am still holding on 24 mins later and countin