I was rear ended by a taxi cab. I have a police report and an estimate. After four months of waiting the cabs insurance denied my claim.

Hire a lawyer, and sue the cab company and the driver, if necessary.  Take the insurance company's letter (all of their letters, from the beginning, if you still have them), and the accident report, a copy of the estimate you got and the statement you submitted, to the attorney.  I have a feeling that you might not actually need to file the suit; a lawyer's letter can often get an insurance company to "reconsider" a position they have taken, which they have a pretty good idea won't hold up in court.

Your attorney might find that denial letter very interesting.  In New Jersey, if an insurance company fails to deal in good faith, they can be sued for that, and the damages usually include attorney's fees.  Denying a claim against their insured for a tail-end suit would take some unusual facts to justify, as long as the policy was in force at the time.