Please tell us why you parked on the double-yellow lines.
As you've lost the discount option, there is no point in paying-up immediately. Please post a GSV link to the exact location where you parked.
If it turns out from our investigations that you should not have parked there and the PCN was correctly served, then as a fall-back I would suggest you submit representations stating you misunderstood the meaning of the PCN handed to you by the CEO, as all PCNs you had previously received had been received by post and you expected the same with this PCN.
So advice is do not pay at the moment, but let us investigate first. You have 28 days from the PCN date to pay so some a few days to go yet.