You will regret joining Budget insurance

Please tell me why Budget insurance debits my account a day before my debit order date when I clearly have a mandate with a date agreed for the debit order to run. I phone last month when this happened and was assured it won't happen again, guess what today my account went on a negative balance because Budget insurance decided to debit my account a day before pay day. What nonsense is this? Can someone fix this, is it to complicated to understand what a debit order date is????