debit order

I have 2 loans with Old mutual finance, this is fairly new, the problem I have is why my account is debited before the agreed date which is the day my salary is paid. My account is now in arrears, I made arrangement since the beggining of this month, I was assured that this month it will be on the 20th but debit order went off on the 19th, it was unpaid I incurr bank charges since june because of OMF, I was then given a very *********** person Lungelo who could not care about my query he does not answer my email, if he does after I made numerous calls he just quote irrelavant sections of agreement that has nothing to do with debit order date, I asked for the full settlement amount to be taken today but because of Lungelo and OMF pathetic incompetency this was not done.