What reasoning have they supplied?
Your next level of appeal is to Transport Focus, which has a role to play if it appears the appeals process laid down in the regulations might not have been followed correctly.
If you don't pay, they add on charges and send increasingly nasty letters, but ultimately have to pursue the debt through the civil courts, which gives you a further opportunity to dispute its validity - it will cost you more if they do this and win, but they don't always bother going to court.
Your next level of appeal is to Transport Focus, which has a role to play if it appears the appeals process laid down in the regulations might not have been followed correctly.
If you don't pay, they add on charges and send increasingly nasty letters, but ultimately have to pursue the debt through the civil courts, which gives you a further opportunity to dispute its validity - it will cost you more if they do this and win, but they don't always bother going to court.