. . . I'v started a re-scan of the blockchain but I was given a new address in the process . . .
How exactly did you start the re-scan? It seems unusual for a re-scan to give an additional address...
Is the original 12A4Zz28AZKptJLLYkcbwrvNy6YbicSv8Z address still listed in the "Receive Coins" tab (so you got an "additional" address), or has the 12A4Zz28AZKptJLLYkcbwrvNy6YbicSv8Z address been
replaced by the new address?
If it was replaced by the new address, this would be a bad sign, and I'd be hoping that you have a backup of the wallet.dat file from before you started the "re-scan".