Ok, I turned the water supply completely off, so I thought, to change the toilet fill valve and to my supprise the water came gushing out? I then had to run in a Lightning storm to shut off the main. My question, why would it still be running after I had shut it off?

Because shut off valves go bad. It makes no sense to try to fix or rebuild them since they are only about $8, get anew one that matches you old connection.

I am with Bob angle valves are cheap and easy to replace, shut off the main and change the angle valve see the image, good luck.

John

I agree with both experts. It's a good thing your main shutoff still works. Simply replace the toilet stop, or remember to shut off the main when working on the commode.