So- I'll pose the question from the other side because I've been in the position before- do you have any moral obligation when you know for a fact that a paying customer is not using the service you're providing?
My gut would say it's not really your responsibility to prompt the cancellation as long as you're not actively trying to make it hard to do. That is, in this situation you'd be accountable but not responsible.
On the flip side, as a consumer, doing something like automatically pausing a subscription if it's not actively being used would make me think highly of your company
I think very highly of fubo precisely because they warn me to cancel my sports add-on packages once the season for the things I regularly watch has passed.
I've often thought this with digital streaming services - a law that said if you charge for the Month of January and it shows at the end of the January that not a single stream even started, then you can't charge for the next month. Not holding my breath.