Refund policies vary from one company to the next. Contact the insurance company for details, all of which should be included in the packet you received with the policy.
You probably won't be able to get a refund for past months insurance coverage, but if you are going to cancel your policy then you should be able to do it. Call your insurance and say that you are canceling your policy and that you would like your money back.
You need to call your agent or insurance company. Whoever you pay your premium to. I'm assuming you cancelled your insurance and are looking for a refund on the part of the policy term that was not used. Sometimes this takes 30 days from when you cancelled your policy. If's for an accident still call the insurance company.
If you cancel your automobile liability coverage, notify insurer as soon as possible in order to realize the quickest and highest refund of your unearned premium.