Yeah, I had the same problem with my GTA V pre-order. Basically, the PSN wallet doesn't take your money until maybe 1-2 days before the game comes out (or maybe on the day, depending on when you pre-order), and so if you don't have enough funds in your account it won't make the actual transaction unless you change the 'Automatic Funding' setting to On. This way, it will add funds by itself. Learnt this the hard way and missed out on my blimp in GTA, and after a lengthy phone call with PSN staff they basically told me to cancel my pre-order (since money wouldn't get taken out any more, thanks to automatic funding being off).
tl;dr. If there's no unlock date on the game, check that money has been taken out. If not, cancel the pre-order and purchase. Yes, this is the only way.