debit order on a wrong date

i am their client for nearly 5 years and all along my debit order date is the 20th but on saturday i received a notification that they have debited my account for the monthly payment of my motor insurance,to my suprise this is the first incident and i want an explanation as to what happened and if there were changes why am i not notified about them,this is my credit record that is at stake.what a dissapointment.