Unauthorised debits

I need some help please so i only find out today that car track is tracking you bank account as well. So when ever money goes in your account they know about it. They can debit your account when ever they want too.is this right they can debit your acount on any given day.Does this sound correct .You as the individuals can put a stop order on and they can just change the amount and date and they can debit..How is this legal can anyone just resond to this please