PSN refund but can still play game

I purchased Fifa 14 on my Europe account a couple months ago and then I sold my vita and I asked Sony for a refund, and they did give me my money back but I never deleted the game out my MC! Forward to today and yesterday I purchased my vita slim, I pop in the MC and BAM Fifa is still playable.. Is this a error by Sony? Can I keep it? Is it illegal to keep playing it?