I put the temperature to 70C on my mini mat and it switches to 25C almost immediately. What's wrong?

The first number you see when you turn the dial is the desired temperature. In a second, you see another number – it’s the current temperature of the surface. 

If you continue to rotate the dial, you will see the desired temperature again. 

When you stop to rotate and set it, the controller display shows the current temperature again. It will slowly go up while the mat is heating.