a3 locking problem

Hi i have a 04 plate a3 and for some or no reason my key fob decided to randomly stop workin so i did the obvious thing and changed the battery still doesnt work so i tried the door lock and tht just turns and doesnt lock it the door lock button inside the car is working fine can ssomebody please advise me on what to try as my car doesnt lock and my area of residence is not the best any help is better thn no help thanks everyone