[Matty4]

First thing you did wrong was admit to speeding....even if it was a different speed to what they alleged. You yourself have just proven the offence, not them.....game over.....unfortunately for you.
Secondly, he showed you a number display on the rear of an electronic device, that is not proof of the offence. Did he clear the display from the last infringement issued?
You need to ask them to show where on the device that it was YOUR car speeding. They can't.