If the borrower has been paying flood insurance for 11 years the property may qualify for grandfathering. Review the grandfathering rules in the Mandatory Purchase Guidelines. If the property does qualify for grandfathering the policy can be left as Zone C.
Insurance agent argues that if they say they will cover any flood claims then why does the policy need to say zone A?
Unless the agent gives you something in writing guaranteed by the insurance company his word isn't worth squat.
The determination should be based on the legal description of the property if there is an address discrepancy.
If the agent refuses to change the policy, if A is the correct zone, then you should report him to FEMA and to your state's Dept. of Ins. Also show him the following letter.http://bsa.nfipstat.com/wyobull/2008/w-08021.pdf