APPLE IPHONE 5 16GB BLACK LOCKED ON O2 BNIB ?

HI I HAVE A IPHONE 5 BNIB FOR SALE BOUGHT YESTERDAY FROM GUMTREE THOUGHT IT WAS UNLOCKED TURNS OUT ITS LOCKED TO O2 NO GOOD TO ME SO LOOKING FOR A QUICK SALE NO SWAPS OR TIMEWASTERS LOOKING FOR 530 TO GET MY MONEY BACK NO LESS CALLS OR TEXT PLEASE YOU WILL NEED A NANO SIM TO TRY THE PHONE AS I DONT HAVE ONE COLLECTION ONLY