Assuming you have submitted a formal appeal, do nothing, they have to respond to your appeal within a deadline, and they’re on a fishing attempt to get you to reveal who the driver was.
In due course they’ll reject your appeal with “after careful consideration” rubbish, but also supply a POPLA code.
What other documents were sent with the Notice to Hirer? This is important, and the answer is probably “none”. You will therefore appeal to POPLA on this basis, which I am guessing you did not in your appeal to CUP. Just so we are clear, what did your appeal to them say?
Read sections 13 & 14 of
An Act to provide for the destruction, retention, use and other regulation of certain evidential material; to impose consent and other requirements in relation to certain processing of biometric in...
if you haven’t already done so.
They admit they have not used PoFA so can not transfer liability from the unknown driver to you, the hirer.