Central locking and key not working

[JO175Med]

I have an Audi A3 TFSI 2.0 cabriolet, last week the central locking and car door lock both stopped working at the same time. The door lock just spins around. Anyone know why this would be? I've replaced the key battery and have attempted to reprogram the key but nothing has resolved it. Would it be an easy job to just replace the key barrel? Any advice would be greatly appreciated 

[DavidTdi]

You need to be able to code read the car to diagnose locking issues otherwise it's guesswork.