going into ones bank account without permitoin

Tracker went into my bank account without notifying me their client. they debited me for two months for the current month and for the next coming month prior. our agreement between us was they should debit me for their service on the 1st of each month not any time they wish to do so, this impose a high risk on my bank account. My knowledge is if one skip payment they will have to do an EFT. Not them going into the clients account without at least notifying them. I call this ***** and disrespecting clients.