Leaving it empty!
I don’t think any company would be happy to hear that a customer wants to cancel and may make it more difficult to do so than it is to sign up.
I cancelled my Customer Factor subscribtion years ago after I tried it. Back then it didn’t have enough features for me and I didn’t want to pay for it and wait for the feature I wanted to come out. The owner made it difficult to leave and I received a not so great email from him scolding me about it.
Fast forward a few years and I signed up again and I’ve been using it ever since. I can’t imagine not having Customer Factor now.
There’s a certain something about calling the support line and the the customer factor’s Owner answers or returns calls 100% of the time. Im sure some of my issues are trivial, but not to me at that moment and in a couple minutes he had me back up and running. I can’t see any other software that could fill my needs better.