Free Traffic Legal Advice

You have received a Notice to Owner, not a PCN. An NtO can only be sent after the 28 day period for payment or appeal of the PCN have expired. Who was driving the car on the day the PCN was served is irrelevant, because the law puts responsibility for all PCNs onto the owner of the vehicle. The NtO was served because the council received no response to the original PCN which would have been served to car or driver. As owner, you are supposed to know who was driving the car on the day of the alleged contravention.

Anyway, if you want more advice please read this and update your thread accordingly:-
https://www.ftla.uk/civil-penalty-charge-notices-(councils-tfl-and-so-on)/read-this-first-before-posting-your-case!-this-section-is-for-council-tfl-dartme/

The above also contains info on how to post documents. You have to use a hosting site because this forum doesn't have enough space to take direct posts.

A Notice to Owner cannot be served any earlier than after 28 days have expired for payment or appeal of the original PCN.

I you want more advice you'll have to post the Notice to Owner, and find out something about what happened on the PCN date. As you have an NtO, the discount option has gone, so I recommend you at least submit representations on the basis that no PCN was found on the vehicle, therefore you have missed the opportunity to pay the discount.