I have a wall mounted mixer setup.

I ran the cold tap, and when I went to turn it off again, it wouldn't close.

I ran down to the basement and went to turn off the mains, and the main didn't close.

I tried and tried to get the thing closed but in the end took a big wrench too it (I know, I can feel the cringes from here) it closed, so the water was off at the faucet for now, and only the hot valve was working.

That night I WD40'd the mains a few times and eventually loosened it, the next day, I turned off the mains, removed the plastic cover and then the screw, the handle for the cold valve and then the housing, I then removed the valve.

I took it to a large DIY store and they didn't stock the part, nor could they name it.

It took it to a plumbers supply store and they had the part. Looking at it on the way home I noticed it was bigger, so I tried to fit it, thinking it was just 'newer'.

After looking at a few diagrams for the valve, I think it's a "stem valve" ?
I noticed that a part was missing from the old part and found it was stuck in the pipe? I'm not sure of the correct name for the part the valve goes in, other than calling it the cold feed for the mixer.

I tried to pull it out with pliers, no such luck.

Now the hot water side isn't running either?

We're going to call a plumber tomorrow if I can't shift it, somehow.

!!

Wow I guess this is a busy forum!