Just got an insurance cancellation letter HELP!

We just got a letter informing us that they are canceling our home owners policy because of the condition of our roof!! I'm furious because our inspector, appraisal and a contractor all said the roof was old but in good condition. We're trying to fight the insurance company but haven't had much luck. Has anyone heard of this? We closed on the house in May! I'm afraid when we go to another company they'll know about the cancellation and charge us higher premiums.