You are completely correct that simply blocking access does not make them compliant while they are still storing that data.

But compliance isn't binary. I'm sure the data protection authorities understand the difference between “LOL I'm already noncompliant so I'll just continue business as usual” versus “Working hard to fix this – in the meanwhile, let's prevent covered Subjects from sending us more data until we are prepared to handle it compliantly.”

But what would you be violating exactly? How could those violations be detected? It seems if the EU is so generous in not wanting to fine and you and walking you through the process, then shutting down would look like a reasonable thing to do if you are still attempting to comply.