Faulty key fob on ford focus?

Please help when i bought my car 8 months ago the key fob would open and close the case and pop the boot from miles away bit by bit ive had to get closer to the car i tried 5 new batteries yet although it opens the boot on that button and locks with the lock button the unlock button just doesnt respond. Im wondering if i have to buy a new key its a ford focus 2.0 51 plate ive tried turning the key to position 2 quickly it hasnt worked the battery is definately new. Can you advise so i can resolve the problem please?