zgbsgshk But they are already on my recruit list
That does suggest they are being sent out. Or at least, giffgaff is paying somebody to send them out, which is not necessarily the same thing.
With single sims, we tend to assume that the garish printing makes them look like junk mail, so if somebody else sees them before you they may think they're pizza adverts and bin them. But it's hard to believe that would happen with a box of 50.
Maybe then try using the other agent link https://support2.giffgaff.com/app/ask/Payback-and-recruits/Missing-SIMs/form/