You might check to see if the trailer is not level. I had this happen to me once and it was leaning to much. Played with the stablizer jacks and got it more level and then the door unlocked just fine...???
After I got it to unlock then I lubed it good and havent much trbl with it since then...
My trailer is a fifth wheel and there is a way to crawl inside going thru the storage bay and up thru the dirty clothes drop hole. Might get a small kid to climb in there and unlock the door from the inside...
If push comes to shove a well placed large screw driver should pry back on the aluminum frame enough to open the door like the thieves do...
Roy Ken