Advice wanted: Pest control company is being a pest

Has anyone experienced something like this? Or know what to do about it?

About a year ago I hired a small local company to get rid of ants invading my house. I looked for one that used environmentally friendly materials.

They told me they did not do one-time treatments. I had to agree to four treatments. If I canceled before having all four, I had to pay a $375 early cancellation fee.

The guy that showed up was evasive about the stuff he sprinkled around the house foundation. I would have liked to cancel but didn't want to pay the fee. The final treatment was in October. I paid the bill and thought that was the end of it. I did not want to hire them again.

In January the company notified me that they were coming out that week to do another treatment. I said I did not want them to come as I didn't want to re-hire them. They told me in that case I owed them a $175 early cancellation fee. I told them I did not owe them a damned thing, that I'd paid for the required four treatments and that was the end of it.

They insist I owe the cancellation fee, and have been pestering me with emails, phone calls and letters. I don't answer them.

I looked through my paper files and computer files, and can't find any sort of paperwork or contract. I always file stuff like this, but there was nothing. I do remember signing something the guy from the company wanted me to sign. I can't remember if it was on an ipad or paper on a clipboard. This is driving me crazy. Did I have something in writing from them or not? My memory isn't as good as it used to be.

There was some kind of agreement of mine on the company's website, but they deleted my account so it's no longer there. In other words, I can find absolutely no proof of what I did or did not agree to. I clearly remember being told I had to agree to all 4 treatments and pay for them, which I did.

I don't feel I owe them anything. This ridiculous fee is for the privilege of not re-hiring them. Why should I pay for non-service?