You can cancel anytime with 30 days notice. We do not lock you into long term contracts.
Refunds are not given for work already completed, including list building, copywriting, and infrastructure setup. If you cancel mid month, you are billed for that full month, since the work for it has already started.
If something is not working and you are thinking about cancelling, talk to your campaign manager first. We would rather fix the problem than lose you as a client.