Playstation prepaid card no longer wanted?

My brother asked for a Sony / Playstation prepaid card for Christmas. Now that I bought it, he told me that he didn't need it anymore.

Is there any way to get rid of or sell these prepaid cards or is that not allowed? Spent 40 euro (2x 20 euro cards) and I'm a little stressed now.

If you were you would upload them to ebay for 15 euro each.