Are airlines under-compensating you?
First read this article by Christopher Elliott dated on April 19th, 2014. Yes, it is dated, but it is still relevant. The link to the article is found here. Christopher is the Go To Man with problems that need resolutions. His contact page is here.
AirHelp is a company that works to get your deserved refund back from the airline. There is no upfront fee. They take a commission from what they can recover on your behalf. They can assist with flights up to 3 years past. It is simple to start the process.
Click on the name for the link.