Can I sue a company I used to work for (as opposed to being a customer), for advertising a product and selling something else?
How would I go about contacting the California Attorney General's Office? Can I write a letter? Can you provide contact information, please?
No. Your question is really whether an individual has "standing" to bring a lawsuit under California Business and Professions Code section 17500, part of California's Unfair Competition Law (UCL) which prohibits false advertising. Until 2004, individuals or groups that never suffered any loss or harm could sue on behalf of the general public without satisfying traditional class action requirements. However, after the passage of Proposition 64 in November 2004, California implemented important procedural changes to Business and Professions Code Section 17200 and Section 17500, requiring a plaintiff to show that he or she suffered an actual injury and lost money or property as a result of such unfair competition.
In summary, you can report the false advertising to the California Attorney General's Office to prosecute a civil action for the false advertising under California's UCL. But you yourself cannot be the plaintiff or a class representative in a class action against your former employer.
Go online at http://ag.ca.gov/consumers/general.php and take it from there.