If you read the EN, you'll see you have two options, (1) pay-up. or (2) submit representations.
So all you have to do now is submit reps stating you never received the original PCN and therefore have been denied the option of paying the discount, and ask them to reinstate it.
HOwever, if you want help to possibly get the PCN cancelled, hold off from submitting reps until we've given advice. You therefore need to unblank the EN you've posted. Only blank out name and address. Of course there may be no possibility of an appeal but at least you'll know you haven't paid £130 needlessly.