App disappeared from Purchases list?

Hi, I bought and have been playing GTA: San Andreas since around its release on the Mac. I tried to download the 4GB update yesterday but had some internet issues and it kept cutting out. Eventually the download finished, but when I went to open the game it came up with a message saying: "“Grand Theft Auto San Andreas” is damaged and can’t be opened. Delete “Grand Theft Auto San Andreas” and download it again from the App Store." I assumed my internet connection cutting out every so often had caused something to mess up. I went back to the App Store to re-download the game to find that San Andreas wasn't on my Purchases list.

My question is, how can I get the game back without having to repay? I don't have the recepit Apple sent me but I do have proof I've owned the game because the icon is still on my Launchpad and get that error message.

Thanks in advance.