Check all your alarm fuses to start with obvious but overlooked!
Take of your drivers door skin a few screws on the edges and clips holding it in, have a look on the right hand side of the door there should be an extra locking motor fastened into everything somehow
either by rods to the original vw actuator or locking pin these may have worked loose?
If not with the door open get a screwdriver and click the actual lock over so it is as if it's closed onto the door pin, take your remote fob and press it you should see the motor move up and down when you lock/unlock if it does but doesn't lock you might need to tighten it up a bit or adjust it, if not have a look how many wires it has it'll either be a 2 wire or 5 wire motor. Go to an autospares shop and buy a replacement plug it in and fix it in place and away you go.
If the above doesn't work post back up, cheers