Total loss disputes are common.
The value of your vehicle is very important to you, but it may not be as important to your insurance company or the insurance company of that guy or girl that hit your car and totaled it.
There are some options to help get a fair value on your vehicle.
The most common and accepted is to employ the services of a non-interested professional. If the professional is truly a non-interested expert, then their opinion should be based on accepted appraisal methods and proper training and experience. The value you get from an independent appraiser should be in line with the actual value of your vehicle as it relates to the terms of the insurance claim.