If he cancelled you should see the cancellation logged in CBSubs > Notifications and/or CBSubs > History Log. It's possible to expire before an auto renewal if a grace period hasn't been configured for plans as it can take up to 3 to 7 days sometimes for a payment to clear. Please also be sure your install is up to date.

I recommend asking how he cancelled and where exactly as it does not sound like he went through normal cancellation process. Recommend also asking when exactly he cancelled. He would not be entitled to a refund for services used, but I recommend refunding any months that he did not intend to be subscribed (e.g. if past 2-3 months were supposed to be cancelled I recommend refunding those).