Wooah!
Firstly, it is not an offence and so NIPs have absolutely no relevance in this matter.
Secondly, any claim for money is a civil Penalty Charge and NOT a fine - only a court can issue a fine!
The notice the OP has received is a claim that there has been a contravention of the order that covers the use of the DRC. They are claiming that on the day in question, someone has used the crossing and that the fee (the toll) has not been paid. As they do not know who the driver was, they have sent the notice to the Registered Keeper, who in law is now liable to pay the outstanding charge. The RK now has a legal obligation to either pay up or, by following a particular process, exercise their right to appeal against the charge.
THIS A SERIOUS MATTER AND ONE THAT THE OP MUST NOT IGNORE. THERE ARE TIME LIMITS THAT NEED TO BE OBSERVED BUT HELP CAN BE PROVIDED IF THE OP WISHES TO CHALLENGE THE PENALTY CHARGE.
FAILURE TO TAKE APPROPRIATE ACTION COULD RESULT IN COURT ACTION AT SOME POINT IN THE FUTURE.
It is my view that all civil penalty charge notices and private parking charge notices should be challenged as there are often numerous legal errors made by those issuing the notices. Unfortunately too many people fail to understand the legalities and are effectively bullied into coughing up because of the intimidating and threatening nature of the correspondence received from outfits such as the DRC.
OP - AT THIS TIME DO NOT PAY ANYTHING AND DO NOT MAKE CONTACT WITH THE DRC ABOUT THIS NOTICE. I am more than happy to help you out. Send me an email and I will take you through the options.