how to open a upc door that slammed shut?

my upvc kitchen door slammed shut, know it will not open, the handle works ok locking the 4 bolts as does the lock. it lock,s & unlock,s, it seems to be jammed just where the latch is,yet the handle is free & will move up & down,the door is probably 12 yrs old, but look,s & worked fine, up until slamming shut with a gust of wind blowing through,the 4 locking bolt,s are free and working, as you can push against the door at the top & bottom & it open,s up slightly,?? many thank,s hope someone can help.