Call blocking problem

For some reason one particular phone number is blocked on my Fairphone 1 and I can’t receive his phone calls. I can’t work out how to unblock it. Can anyone help?

Did you accidentally block them via the people app?
To check: open the people app (the one with the stack of cards with a face on the top card, not sure what names it has in other languages) and find this person’s profile. Open the profile (i.e. tap on it) to bring up their details. Tap the menu key (the left most key of three keys below the screen area) - this will bring up a menu. Check whether ‘Block incoming call directly’ is checked (obviously it shouldn’t be if you want to receive calls from this person).