Thank you for your question. I look forward to working with you to provide you the information you are seeking for educational purposes only.
If the accident was not your fault, then it should not have been charged to you as a fault accident to cause an increase in your premiums. You need to start by sending a written appeal letter to the insurer with a copy of the police report and witness names to show this accident was not your fault and as such holding it against you is breach of contract. If they refuse to reconsider, you need to file a complaint with the Department of Insurance against the insurance company.
Finally, if they cannot resolve this matter, I am afraid you would need an attorney and would have to file a civil suit against the insurer for breach of contract for improperly raising your rates for a non-chargeable accident.
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This is NOT the practice of law nor is it legal advice to you, it is merely educational information for you to use to seek out a licensed attorney in your state to get actual legal advice from them. Please use sites such as http://www.martindale.com or http://www.lexmundi.com or http://www.hg.org to find a local attorney to get actual legal advice in all matters.