This is a pretty normal thing to happen. Most (all?) TOCs use automated systems to deal with the bulk of delay repay claims, which automatically pay clearly valid ones and automatically reject clearly invalid ones. Those require very little human intervention and as such tend to be paid in a fairly short time.
Sometimes the system will put claims into a queue to be reviewed by a human, which can take quite a while (sometimes a few weeks), but they haven't forgotten about you and it will be paid eventually. I imagine this occurs if there is something unusual about the claim - but judging by what's happened to my claims in the past, in some cases it also seems to do it randomly, presumably as a sort of spot-check to make sure the system isn't being significantly abused.
I doubt there is much you can do to accelerate the process at this point, but if you haven't had an update for a while you could consider emailing them to chase.
However, if you travelled on a 2 for 1 offer, what exactly are you claiming for? Surely one of the tickets was free and therefore no compensation is due? Or was it actually issued as two half-price tickets?
