do u know how u join their slack?
my account enhanced already but i have no idea how to join there
iam agree with u that should be moved to spam folder
actually i got the same problem with my account on HiBTC and coinexchange
i accidentally marked their mail as spam too
and i no longer received anymail from them, contacted their support and they fixed it
look like this zendesk support no have solution for my problem
Unfortunately, the Slack invite has to be sent to you by them, there's no automated mechanism yet (they have been saying they will look into one for ages), even I have never received the invite. But you can just keep trying to bug them on Support and on their Social Media, unfortunately the only way these days to get your problem resolved.
What email provider are you using? It's strange that marking as spam blocks it, I don't know any provider that works like this. You've already added to contacts and cleared your spam inbox. Can you try "whitelisting" emails and domains bittrex.com?
OR, use your Bittrex account settings to add a new email? Until problem is resolved?