Hi @SteveS,
To join the new team, can you try logging in to your main account, and then clicking the team invitation link or the invitation link in an email for the team you want to join?
If you're logged in you should automatically join the team with that account, we're trying to add a "Sign In" option to the account creation page soon.
You should be able to "Switch to Team" after you join the other teams with your main account.