Hi I have replaced the flush system of toilet and now have problem that cystern won't fill up. The screw on the valve just keeps turning with nothing happening, so thought I would replace this and flexi pipe, however in spite of turning water off at main there is still water coming out of the pipe so scared to keep working on it in case I flood bathroom

Open a cold water valve at sink or tub that is closer to main shut off. This may releave pressure at toilet so u can work on it.

If not, the main shut off valve will have to be replaced. If u have well water, shut off pump.

If u have city water, water will have to be shut off at curb and must be done by a licensed plumber or city water department.

Chuck