You most certainly can and they have to provide you the data. GDPR is about you as an individual and the login itself is irrelevant. Chances are you'd most likely hit the same wall when talking to the customer support.

legal@ is a great way to talk to a real human.

Well it’s also a great way to never get a response again until you meet them in a courtroom :(

In theory yes, in practice Google will stonewall you just as usual and none of the regulators is interested in enforcing the GDPR enough to get this pushed through, so in practice you're still out of luck. Here's a real-life example: https://ruben.verborgh.org/facebook/

Very interesting anecdote. Is there a conclusion to the story?

We seriously need some stronger consumer-protection laws in those areas. We live in a digitalized World. To some degree those accounts are a part of peoples lifes! Companies should not be able to simply take those away without any good reason and any way of legal recourse.