Drivers door lock barrel

Hi Guys,

I am a newbie and wondered if anyone can give me some advice?

I have a 56 plate octavia 1.6 fsi classic.

My driver lock is knackered (just turning) i have got a new barrel from the dealers at £43.00 (which i thought was reasonable) I have checked on the forum as to how to remove the barrel .

I have turned the screw under the grommet inside the door 3 turns a described, and the barrel will NOT move it is jammed so much I am beginning to damage the door.

The post I have read says not to turn the locking screw too much as the clip will fall inside the door (is this easy to get out?  Other posts say to turn the screw until it stops turning another one says there is another screw underneath which you have to turn I tried this all this does is to stop the handle coming out which one post says you have to pull out slightly.

Baffeled and frustrated. Help please anyone