Sorry, but I missed nothing.
http://www.miragetrailers.com/documents/warranty/cargo-trailers-warranty.pdf
It's spelled in massive, bold letters that Mirage Trailers are warranted for 1 year, not 3. Furthermore, it also clearly states that axles are covered under the axle manufacturer. So, did you try getting in touch with the axle manufacturer before you blew 5200 bucks on repairs?
No offense, but it sounds like you should be angry at whoever fleeced you for 5200 bucks for repairs (not including labor). That's half the price of a brand new trailer for crying out loud.
Also, consider this. Most manufacturers on Earth will immediately void a warranty if you attempt repairs on your own. For instance, many electronics devices have a special seal that breaks when the device is taken apart. Breaking that seal immediately voids the warranty. I can't imagine any manufacturer simply taking a customer at their word that they performed thousands of dollars in repairs without any sort of contact/photos/consultation prior to the work.
If I were you, I would have consulted with Mirage before just diving in and attempting the repair. I've never had a problem with repairs on my trailer when dealing with Mirage.