If your a "hands on" person you could probably check and solve the problem yourself.
Here are a few things you can try to do if your toilet doesn't stop running:
Depending on the toilet start by jiggling the flush handle. If the water stops, you mite need to adjust the lift-chain attachment or the handle.
Still runnin? Remove the cistern cover and check to see if the ball cock (floating ball) is touching the side of the tank. If yes, bend the arm to move the float ball away from the edge of the cistern.
Lift the Ball cock by the rod above the water level. If the water stops, gently bend that rod down until the ball cock (floating thing) is at rest when the level of the water is about 20mm below the top of the overflow hole.
Check if your ball cock (float) is damaged . if its under water, it may be damaged or have a hole so its sinking. Turn off the WC valve on the right or left hand side of the tank and flush the toilet to empty. Unscrew the ball cock (float) have a listen if thee is water inside If you hear water, replace it.
Sometimes the Flush valve (Flapper valve) washer is worn maybe distorted and doesn't seal. This is an easy fix. Just empty the cistern, remove the washer (doesn't cost very much and can be purchased at any hardware store) and replace it with a new one.
Try a few things and see how you go. I have attached a picture to help with whats what.