Broke iPhone 5c and cannot locate synced Apple ID

I accidentally cracked my iPhone yesterday and went to the Apple store to get it fixed. While talking to the tech there I was told to enter my Apple ID so that they could retrieve the information they needed. I entered the one I used on my phone but it didn't show up that it was the one synced to my phone. So I tried an older one that I used to use but that one wasn't synced with it either. How is it possible to find the ID that maybe I used when activating my phone? I have tried the "Find forgotten Apple ID" but that doesn't help. I can't call the support today because they're closed.