The first thing you need to do is find out exactly why the insurance company is denying the claim. Fire is one of the most common perils faced in home insurance, and is included as part of every homeowners policy unless it has been specifically excluded, which is not very likely. Once you know why the claim is being denied, you will be better able to do what is necessary to get the claim settled, if there are any options available at all.
One reason a claim might be denied would be if the policy had either not yet gone into effect. Most insurance companies will have a waiting period on the policies they write, and until that period of time has elapsed, your policy will not pay out any claims. Similarly, if your premiums were delinquent, the insurance company may have cancelled the policy. In this case, you would have received notice of the cancellation well before the policy was terminated. In both cases mentioned here, you may not have any options available to resolve the issue.
Another possible reason for refusing the claim would be if there are questionable circumstances surrounding the fire. If the fire is being investigated for arson, as an example, the insurance company will not settle until the investigation is complete, and if arson is found to be the cause, you may never be able to settle the claim, even if you are completely exonerated of any involvement.
Contact a lawyer who specializes in insurance and find out what they have to say on the matter. Most of the time, your first consultation is free, and the attorney will be able to tell you afterward whether you have a case or not. Even with legal representation, you may not be able to force the insurance company to settle the claim if circumstances surrounding the fire are excluded by the policy documentation.
In any event, you should consider switching insurance companies in order to protect the possessions you still have any your current home.