Debit order without authorisation

I received a quote from ADT a few weeks back and one of their reps. came to my house to explain everything, I did not confirm that I would make use of their services. They have been hounding me with calls everyday, even after I have told them I will let them know when I’d like to proceed. They sent two install. guys to my house whom I’ve turned away. I have now received a bank notification of a debit order which they processed, WITHOUT MY AUTHORISATION!! Beware of this company as they will do whatever it takes to gain customers, even debit their accounts without prior authorisation!