Not if it isn't ethical. You're painting those with the failed payments who didn't cancel of being the ones in the wrong to justify the action taken against them, but heavy handed payment collection of a SaaS they likely weren't using doesn't sound great to me either. How about just doing the honorable thing that also isn't chasing bad clients?
> If the customer doesn't want the service they have the option to cancel.
Would you take Adobe as a customer, with their infamous cancellation dark patterns?