Unauthorized Early Debit

I have two existing policies with Old Mutual, one for savings and another for retirement. Both these policies debit my account on the 25th of each month. Of late I decided to add another policy called Greenlight so I could cover myself, child, and fiancee in the event of death. To my surprise however, Old Mutual decided to debit my account on the 24th for this policy, a day before my pay day. The bouncing of debits reflects bad on my credit standing and my bank charges me no less than R100 for every debit that declines. It therefore follows that Old Mutual should pay for these charges because I never gave them authority to debit my account on the 24th. Unless they can prove otherwise, they do owe me the charges I have now incurred.