You need to contact the police force who sent you the original correspondence, you will have told them your driving licence number when you admitted to being the driver of the vehicle concerned. They will be able to provide this information to you.

You can contact the appropriate Police Force by any of the following:

• If you have it available, using the police contact details on your Course Offer Letter/police correspondence.
• Via the police website
• Call the non-emergency “101” number and ask for the department that deals with Fixed Penalty Notices.

You may also wish to contact the DVLA:  https://www.gov.uk/contact-the-dvla