I just went through something similar. When I canceled my Netflix a couple of weeks ago. I noticed that it would be very easy to restart the subscription for anyone who was still logged in, so I logged out all devices and attempted to remove the credit card. Interestingly, they won't let you remove your credit card unless you have another payment on file even if you don't have an active subscription. I just changed the password so nobody who I previously shared it with could accidentally log back in.

The most ridiculous thing is that about a year ago I specifically bumped up my plan to the more expensive one because we were sharing with some family members. As a result of them enforcing this sharing rule, we ended up canceling and they get nothing from us now.