How do I complain about a rental car company if they won't give any satisfaction?

Omega Rental cars basically told us to get lost when we complained about the fact that they upgraded us to a larger car without our permission. We wanted a small car to save petrol, be environmentall friendly etc. They even took our copy of the rental agreement from us when we returned the car and will now not respond to my emails asking for the name of a manager!How do I complain about a rental car company if they won't give any satisfaction?
Go up as high in the chain of command to the corporate office if you have to. If that doesn't work, every company must get a business license or permit so contact the city's agency that licenses them; the city might also have corporate phone numbers. The company may also be licensed as a corporation with the state attorney general. You can also report them to state consumer affairs and the better business bureau. Of course it is a spin of the dice with government agencies: will they help you or just jerk you around. Finally you can legally threaten to sue them in small claims court for damages. Send them a demand letter by certitied mail. www.16lunchtime42.com.How do I complain about a rental car company if they won't give any satisfaction?
Do they have a corporate office? You can try that or the Better business bureau - local ombudsman ...
I just did a quick search. Check this website.