Under Govt. Code 12940(j) and 2 Cal. Code Regs. 7287.6(b), discriminatory harassment (affirmative oral epithets; physical violence/touching; visual cartoons, derogatory posters, etc.) extends to independent contractors -- even though passive discrimination (failure to hire, termination based upon discrimination, etc.) extends only to direct or leased employees.
Given this background and your allegations, you have a claim of harassment, despite your independent contractor status, but only
if the harassment can be tied to discrimination based upon your race, religious creed, color, national origin, ancestry, physical disability, mental disability, medical condition, genetic information, marital status, sex, gender, gender identity, gender expression, age, or sexual orientation. Govt. Code 12940(a).
As bizarre and unfair as it may seem, if the harassment is "personal" to you -- i.e., the supervisor simply doesn't like you personally, but not due to some underlying legally discriminatory motive, then you would have no recourse on a discrimination claim, no matter how obnoxious and annoying the oral attacks on you may have been.
There are a couple of possible common law tort actions that may apply: defamation of character; and interference with contract.
Assuming that the supervisor made statements about you as if they were factual -- i.e., You're an eff'in idiot, in front of others, then you may be able to make out a slander claim. And, assuming that the supervisor of your supervisor was aware of this conduct, then it's possible that the employer may be vicariously liable for negligently supervising your supervisor. Otherwise, your claim of defamation would be personal to the supervisor only.
And, if the motive of the supervisor was to destroy your contract with your employer, and the motive for doing so, malicious, then you could sue for interference with contract (economic expectations). These tortious claims are generally much more difficult to prove than are statutory discrimination claims. Consequently, many lawyers will decline the invitation to take the case.
Hopefully, you can identify some unlawful discriminatory motive for the supervisor's conduct, because it would make your case much easier to pursue.
For a competent employment rights attoreny referral, see this link.
Please let me know if I can be of further assistance.