I received an invitation to beta test the game in my email notifications. Going into the invitation redirects me to a page from my account relating to Steam playtest invitations but I don't have the invitation there.

Has anyone encountered this problem or know what the official contact details for Deadlock are? Steam support says they have nothing to do with it.

The game developer is Valve, which does not have any official support other than Steam support. Where should I report the problem?