Please confirm that you DID NOT confirm that you were driving in your contact with the operator?
The original PCN is not POFA compliant so they cannot hold you liable provided that you have not admitted to being the driver.
As far as I can see, nobody suggested that you contact the operator to ask for the mugs discount to be re-instated?
This is why it is important that you follow the advice given.
Please confirm that you have not revealed the driver?