Water Valve to toilet will not stop water supply
It is very common for the "stop valve" (the local water supply shut-off valve for a plumbing fixture) to leak by. Over the years the rubber bibb washer either softens to the point that is disintegrates when tightened down against the valve seat, or calcium scale or/and mineral deposits prevent proper sealing. Try opening and closing it a few more times, then use pliers to actually force it closed. Any of the following scenarios could play out:


the water flow will stop*
the flow will not stop*
the handle will break or be crushed and the flow will not stop*

*these scenarios require that you shut off the main water supply to the house/area and repair or replace the stop valve (most likely replace).