Can't get EV3 to work with touch sensors
Are you sure that the button is being completely pressed? A quick test would be to hold the robot and manually press the touch sensor. If the wheels start turning backwards, then there isn't anything wrong, you just need to make sure the button gets pressed completely.

If you're sure the button is being pressed, then it's probably a software problem. It seems like you have a conditional block, is it reading the same port that the sensor is connected to. 

You could make a really simple program that has a forward tank movement inside a loop and make the exit condition for the loop be to exit when the button is pressed. If you put an end block after the loop, the robot will drive forward forever until the button is pressed.

Hopefully one of those options will help you fix the problem!