That young man's experiences are precisely what happened to my friend, although the lad seems to have had more contact from G4S. People aren't turning up because G4S have reneged on the agreed conditions (pay, travel, accommodation).
But the last bit, the reply from G4S about LOCOG increasing the numbers required at short notice reinforces what was said earlier. I believe LOCOG, as well as G4S, are in serious breach of contract. In fact, I know LOCOG are, at least over supply of Government owned accommodation. The G4S chairman took the hit last week in front of one of those pompous committees, but that one reply about contracted numbers tells you where this is going. If the games go off smoothly, there will be a big effort to quietly bury this among the claims of success.