There are several ways in which print credit may have not been awarded or disallowed. For a start, it is possible that the person you have referred has not purchased anything yet.
Then it is possible that they did make a purchase but the print credit was disallowed because their details matched details previously used to make purchases with us.
On the latter point, we have to be very firm, otherwise of course the system could be used to gain an unfair advantage. For a full set of terms and conditions of the referral scheme visit the T&Cs