When did they join?
Do you see the recruit here? https://giffgaff.com/spread/recruits
How many recruits does that page show so far?
Payback is calculated after the end of each month, so if the recruit as this month, then it won't be added to your payback total untill around the 10th of Jan. And then will be paid out, including all other payback in June.
If you have recuited more than 15 members, you are now a super recruiter and no longer get £5 payback per activation. Instead you get a bonus for the second and third topup made by each new member, therfore there is no way of knowing in advance if you will or won't get money for that member, as it's down to if and when they top up. This money is paid around the middle of each month, totally separate to payback.