Free users can only save up to 50 contacts. This limit also includes blocked contacts and Hunqz. Note that if a contact deletes his profile, it still counts as saved.
If you want to save or block new contacts, you'll have to delete some of the existing ones, or subscribe to PLUS.
I suggest also that you navigate to the bottom of you CONTACTS list to find those contacts that are inactive or deleted, so that you won't mind deleting them.