Expected behavior
It should be easily possible to unblock contacts
Actual behavior
I have to add a blocked contact again by typing the mailadress as new contact.
you actually just have to go to settings/privacy/blocked contacts and will get the list of blocked contacts, then unblock them
OK, thank you.
It’s very good hidden 
I think it should be a easyer to find.
probably it isn’t in the best place, at least I didn’t expected to find it in the Privacy menu, related to this, but not the same: Add button to add blocked contacts