What car insurance company has policies that start with the letters HPA?

For alphanumerical policy numbers, check if the letters can give you hints about the location of the policy issuer. PA could mean Pennsylvania. Call your own agent for more information.

I hope this articles is helpful,

https://www.carinsurancecomparison.com/how-do-i-identify-a-car-insurance-company-with-only-a-policy-number/

I let MY insurance company do this kind of work. That's why they get paid the BIG BUCKS. What state are YOU in?

The PA is probably "Personal Auto". H doesn't mean too much. I worked for Travelers for many years and we had lots of Alpha policy prefixes, none of which had a T in them. What is the issue? Uninsured? Your agent should be able to help.