Perhaps the ethical thing to do in those situations is to fight the dispute? Acquiescing encourages bad actors.

Your current course of action is probably still best for your business and sanity, though. Hmm...

I assume you send an invoice/receipt email every month by default, to reduce the chance that a user forgot to cancel and to make it easier for those that wish to. (If not, I think Stripe Billing offers this, though I'm not sure...)

(disclaimer, I work at Stripe, though not on Radar or Billing, thoughts my own, etc)