Hi, it may be that fob does work but just needs synchronised with the car, can't remember exactly how to do it but I found instructions online and the process worked.
Your fob should have a small red light above the buttons which lights up when a button is pressed. Also if your fob has had the casing replaced with a non-original one the batteries can slip out of place causing it to not work, a tiny piece of blutack will hold it in place.
If the fob is faulty, you can buy 2nd hand ones on eBay but you need one with the same code number printed on the circuit board as the original fob, I paid about £20 for one.
If you can't get the original to work I don't know how to tell if it's the fob or the car that's faulty.
Good luck