Debit Order taken before debit order date

In May 2015 we app**** for a personal loan with Old Mutual Finance and we were successful in getting the finance. We signed for the debit order to be taken every month on the 25th of the month but to our surprise they had now tried on 2 or 3 occassions to debit the account prior to the date that we signed for the debit order to be taken, this does not only reflect badly on my husbands CREDIT RECORD, his BANK charges him over a R100 for an UNPAID debit order if there is no money in his account when they try to take the money, this is totally unacceptable, why did we sign a contract for a specific date for the debit order to be taken if Old Mutual does not adhere to the date that we had signed for. This is not the first time that we are experiencing the same problem with Old Mutual Finance and about 2-3 months when this also happened I was promised by the head office that this will not happen again, she will make a note on the system for them to debit after the 25th and not before and this month, they just damn well go and debit the account on the 23rd. Old Mutual will make sure that they pay the unpaid debit order at the bank and also send notification to the credit bureau.