The problem you had has absolutely nothing to do with these kinds of sites and everything to do with the fact that one specific company failed to implement stripe billing correctly so you can cancel your subscription. This technical oversight could have happened with any type of company and makes this comment largely irrelevant here.

This may be an opportunity for Stripe to allow end users to log in and view all the subscriptions they have across all of Stripes client companies. This way you can log into Stripe and cancel that way if the company fails to make it easy for you to cancel your service.