Debit Account whenever they feel like

I bought a car using this ******* financial services.. unfortunate I missed one stop order but not they are not sticking to the date of the last date of the month..they put on the stop order anytime they think they will get money in my account. This results in bouncing stop orders and the they should pay for these charges. I will not be paying the bouncing stop order fees

Agreed date is last day of the month but this month the put their stop order on the 27 of the month August. Why I don't know?.. please help me on this as it's causing lots of unnecessary a charges & issues. stick to agreed date