https://bitcointalksearch.org/topic/how-to-file-a-proper-legal-complaint-against-coinbasecom-375245
Coinbase Inc. is not a California based company. They are in fact based in Oregon.
After filing a complaint to the attorney general of DoJ of California, I have subsequently received a letter in the mail recommending that complaints against Coinbase should be redirected to DoJ in Oregon. Here is the company details:
Coinbase Inc.
14525 SW Millikan Way #26680
Beaverton, OR 97005-2343
(415) 843-1515
The complaint can be filed online here:
https://justice.oregon.gov/forms/consumer_complaint.asp
Hope this helps!