If the blockage is in the toilet try plunging it vigourously with a mop while the pan is still full with water.
If it still doesn't clear, it could be the toilet isn't blocked but the drain is, in which case it needs rodding.
Check also that the outlet pipe at the back of the WC is running downward, when it had been installed, as a pipe that runs level or upward will block on and off forever.
Best policy
February 2011