Monitronics Unlawfully charged my bank account Nationwide

On the whole this company has provided good service.  However, one time I did not send in my monthly payment on time.  Note that I was not on an automatic payment plan.  Nevertheless, the company managed to withdraw the payment without my permission to either them or to my bank.  They obviously got my bank information from the submitted check  but how did they manage to persuade my bank to give them the payment without my prior authorization?  I know I should have pursued this further at the time but I didn't.  I would advise looking at alternative alarm companies if you're not on the hook with them already.