A gentlemen with an english accent called me last month from an SEO company and said they will increase our rankings on google and because many other SEO companies haven't fulfilled their promises by getting their clients a high ranking this is why they are offering one month free trail and by the end of this month I will see the results and then if I wish to discontinue I should let them know otherwise the service will continue running and they will start billing me. I agreed and requested them to mail me the details so that i could have a contact email to cancel the service if I wasnt satisfied. Its been a month and i received no email and I strongly feel that they are going to bill me and I have no way to cancel. Btw when i try to google our website it still doesnt appear in the first three pages based on the keywords i gave them.

Firstly this should serve as a warning to others...

Is there any advice to safeguard myself from being billing and having to pay the amount at the end of the month?