You should be able to still block 'unknown' callers. Check in settings of either the phone app or the contacts app. Different devices have it in different locations. It will usually have a setting for blocking unknowns. Meaning anyone not in your contact list, and also one for blocking private numbers. If you want something that blocks more, or gives you more options for blocking (sometimes even texts which are not covered with call blocking) then there are quite a few free apps you can get for that.