Attempt to debit home loan before due date.

On 18th Dec 2015, my bank account had a transaction titled EDO TRAWLING ATTEMPT for an amount exactly matching my Nedbank home loan debit order - which fortunately did not go through. My debit order date is the last day of every month. What I don't understand is why is my bond amount which is not yet due being attempted to be debited by yourselves almost two weeks before due date?? Last year at roughly same time you attempted to do the same thing. Is it Nedbank's policy to attempt to process their client's debit orders before due date during December?? Surely this cant be right!! An explanation for this disturbing trend will be most welcome.