13 pin plug newbie confusion - where's my problem?

Hi all, I’m a newbie to caravans and to this site so please go easy on me.  Unfortunately I’ve yet to even hitch up my van and already I’ve got a problem that I can’t solve, so I’d really appreciate some pointers.  It goes like this (sorry it’s a bit long, please bear with me..)

Last week I had a tow bar and ’ECS’ brand dedicated loom fitted to my car in preparation to pick up my caravan next weekend. All was fine until I attended a CC Practical Caravanning course at the weekend.  While I was there I couldn’t get a 13 pin plug to connect to my 13 pin socket. I tried two different plugs, and neither was a fit. According to the two instructors on the course the problem is with the socket and I have no reason to disbelieve this, except perhaps for the discussions on this site and elsewhere about the possibility that the 13 pin plug can become misaligned.

This morning, I called the fitting company and spoke the guy who fitted the towbar.  He took the time to talk me through the socket while I looked directly at it. To give you an idea, with the plug cover hinge at the 9 o’clock position, the locating block is at 3 o’clock, and the three locking lugs are at 1, 5 and 9 o’clock. He confirmed that this how it should be, and he said that it’s all one mould so it wasn’t possible for it to be misaligned anyway (unlike the plugs, which can be..).

This evening, in an attempt to save my own sanity, I bought a new 13 pin plug (actually an adaptor) and it’s clear that this won’t  fit either:  With the plug in the fully unscrewed/unlocked position and with the pins facing away from me (so to match the alignment described above) if the aligning block is at 3 o’clock , the locking lugs are half past 1, half past five and half past 9. The range of movement of the plug lock doesn’t allow me to arrange the alignment block and the locking lugs in the right configuration for the socket.   Also, in the locked position, the large flat for connection to the spring cap is at about 8 o’clock again when the locating block is at 3. Sorry if my terminology is a little rubbish...

I have simply no idea what to do next. Does anyone have any clue where I’m going wrong? Does anyone else’s socket look like mine?   Help!  Thanks for reading.