You can respond with the following;
I am the registered keeper.
As your notice is not PoFA compliant I will not be accepting any liability for the outstanding parking charges.
The driver is not known to you and I will not be providing any driver details.
Your options are;
Cancel the notice
OR
Waste further money by providing an IAS referral code.
I am sorry that I am unable to help you further.
Many thanks,
xxxxxx xxxxxxxx