the inlet coming out of the wall for just about any residential toilet has a shut off valve. if water keeps rising after flushing turn that

also to fix a clog after shutting off the water, grab a bucket or a clean garbage bin and fill it with hot water. then dump that water in the bowl all at once. the hot water helps break things up, and doing it manually you can both avoid overflowing and dump in a lot more water a lot faster than flushing normally can. fixes 90% of clogs ime, takes less effort and makes far less mess than a plunger