Red alert, door open alarm won't go away

Hi guys,
This is my first post and I'm not sure whether it's an electrical or mechanical fault so forgive me if I've posted in the wrong section.

My 56 plate c220 started displaying the red dashboard alarm telling me the drivers door is open,
I've tried slamming the door making sure nothings caught in the mechanism and turning the car off and on. No luck, it won't go away.

 

Check correct operation of the driver's door courtesy light pin switch. The pin may be faulty leading the car to think the door is open. Do the interior lights go on and off automatically when the driver's door is opened/closed?

 

The should be the door switch, they can get dislodged on the C class. It could be on the A pillar lower half or just underneath the lock keep on B pillar.

 

Hi and thanks for your reply, No idea what the light pin switch is do you have a picture of one? Yes the lights automatically come on when the door is opened so I've flicked the switch to permanently off for now

 

So I got a friend to show me where the door light pin was and turns out there's a plastic cover that surrounds the door lock mechanism which presses the pin down when the door is closed. This was missing, found it on my drive when I got home and fitted it back on.
Thanks for the replies guys.

 

I have heard it is the seat belt that gets caught up in this and knocks it off.