I'm looking for reasonable Insurance on a vacant for a period of 6 months.

I'm in the same boat as you, closing on the 15th and no insurance agency want to insure me.

Was he licensed and insured when you hired him? 

But property and flood insurance is! 

If so, you can get title insurance for less than $200 that would find any issues and protect you moving forward. 

My immediate concern however is how this cancellation of insurance will affect my mortgage on my loan.

You could also ask the bookkeeper which CPA does he/she collaborate with and then verify the competence level with with the CPA.If you are concerned about the safety of your financial documents, most cloud based accountants use software (Quickbooks, file sharing services, etc) with bank-level encryption. 

Is there an ethical way to demand payment or can you chalk up the loss rent on insurance claim?

And if you have an attorney, he should have caught the omission and maybe you can go after his E&O insurance.

Apparently there is what's called the master insurance policy that is supposed to be put into effect first before any secondary or personal insurance can be used.