Terminix billed for unauthorized service. Largo Florida

I canceled my lawn spray service in July 2014. They treated my lawn in August 2014, then billed me $128. I called and complained, they said they would credit my account. They said they didn't process the cancelation in time to cancel the service call. I felt 3 weeks was sufficient time. In September of 2014 I received another bill, and I called again. I was assured again my account would be credited, it has not. I wrote them and filed a claim, their response was simply"Claim Denied". I have never been able to talk to a manager, or get a call back. My written response to them was "After reviewing their bill for unauthorized service, and trespassing on my property, their bill has been denied." They have now filed a negative comment on my credit report. This should be illegal and penalized. I had no other issues or late payments with them for over 10 years. If I knew this is how they do business I would have fired them years ago. They actually had the nerve to offer me their same service at half the price I was paying. My response was, " So how many years have I been overpaying you?" In my opinion they use deceptive trade practices, lie, and are nothing more than a bully. I am still waiting on them to mail me correspondence proving their claim. They do acknowledge I canceled in July, and serviced my property in August. But I must pay because of their incompetence.