Plays blu ray will not play dvd

http://www.docs.sony.com/release/BDPS350_US.pdf

Above is the us version of your manual.
I suggest you look at the dvd/bd settings on page 46.
Check the manual for the discs you cannot play.
Check that the region code of your dvd matches the one on the disc..

If you want to mail it and must have a receipt
1.Find out the way they paid for your gift,if its with cards, they will have a record on paper or the internet of the spend.
2.Also check with the shop if you can prove that it was bought there, and they may issue you a copy receipt.