Can they look up my return on my debit card, I can't find receipt

I've never done it myself, but i'm sure you can. You can bring bring some other kind of proof of the purchase and they will work with you.

I believe they will give you a store credit for a return without a receipt with a picture i.d., but only a couple of times... not repeatedly.

You should be able to pull up the purchase of your bank statements to help them get a transaction number.