they certainly can’t block me from reporting that it isn’t working, for them to accept it.
Is r/help run by admins? I can't remember.
Anyways, while I agree that they can't ignore your request for your data under the GDPR, i don't think there's a law saying that they have to acknowledge their website being broken. Technically it's fine for their system to be broken as long as you're able to submit a GDPR request (even if only by email), unfortunately.