You can contact Admiral Insurance at their phone number which is 856-429-9200
You can also contact Admiral Insurance through mail at their address.
Admiral Insurance Group
1000 Howard Boulevard
P.O. Box 5430
Suite 300
Mount Laurel, New Jersey 08054
They also have a contact form on their website.
https://www.admiralins.com/contact-us/
Cancelling a car insurance policy with Admiral is relatively straight forward and you'll be able to do so either online or over the phone.
The issue is that whether it's inside or outside of the cooling off period, you'll be charged a cancellation fee, which can be a real hit, especially if you had a telematics policy.