Have you tried just signing in to the instance. I know when I applied to join one of the instances, I never received an email telling me that my application had been accepted. So after a couple days, I just tried signing in, and it worked.

feddit.uk is an active one, if you don't have any luck at the café.

Have you tried just speculatively logging in with the details from your first sign-up? There've been a few issues with emails not sending to certain providers, I don't know the technical reasons, but you might be accepted and just not realise.

Might try just logging in, I have heard several people say that they didn't get an email from the server they signed up for but when they went to sign in, it let them

Did you check this post https://lemmy.cafe/post/102749
Confirmation email could be in spam.

Some instances have an chat on Discord or Matrix for help, check if there's something

Probably just the mass amounts of people coming from reddit.