If your toilet is running continuously, the problem is probably the water pressure.
Indications that this is the problem would be hearing the toilet run continuously, the need to jiggle the toilet handle to stop the flow of water, or leaking.
Look for water flowing down the sides of the toilet bowl, a long time after the toilet has been flushed.
This is a good indication that the pressure is too high. If so, a pressure regulator should be installed to monitor the water levels.
However, it could be that the flush valve needs repair, especially if the toilet flushes by itself. This flushing is response to leaking and the toilet filling up with water.
A local professional plumber will be able to solve the problem.