Often paper gets stuck in the seat of the valve and keeps the valve from closing. Take a coat hanger or equally heavy piece of wire and bend about a 1/2 90 degree on one end and form a handle at the other end that will allow you to work the short end in the valve seat while the valve is held open.
To prevent this in the future make sure that everything in the toilet is Floating free before stepping on the valve. This is a common problem with kids as they just step before checking.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles