Wrong debit date

I am very disappointed and annoyed. I took the policy this year January and asked to be debited on the 20th each month because that is my pay day.. Avbob keep debiting on the 19th, I asked them to stop but still going on.. The debit runs while there is no money n this impacts my credit coz it put my account overdrawn n the bank charges me.. This has to stop avbob.. This happened today as well n 20th is not even a weekend.. I need this rectified asap.. ***