iPhone 4 Backup overwritten when exchanging phone

Hi guys,
There seems to be a monumental flaw in Apple's backup procedure for the iPhone 4. I hope there is a simple solution.

I dropped my iPhone 4 in the sink. Wasn't working properly but did manage to get a backup out of it. Took it to Apple store today where they exchanged it for a fee.

Got home, set up new iPhone and went to restore from backup and its gone! Been overwritten by a backup 5 minutes ago of this new BLANK iPhone.

Seems madness, surely I should be asked to delete/overwrite an old backup?

Lost all my SMS, camera roll etc.

Is there any way for restoring this old backup (from yesterday!)? I'm a PC

Thanks in advance.