I signed up for this a while ago, intending to cancel by the end of the month, just due to my travel patterns. I forgot and my card got charged yesterday. Technically (according to the email that they send you when your sign up) the last day that you can cancel and not be charged for the month is on the billing date (yesterday). But I chatted using the support site and they canceled and refunded me with no pushback.

Personally I think that it's kind of shady that they don't send you an automated email a few days before they bill you, but it's nice that customer service will make it right if you forget.