Kendall Jenner -- Shut Down By 'X Factor' Boy Band

Sometimes, but not often ... someone says no to the Kardashians -- just ask super mom-ager Kris Jenner who recently tried to hire "X Factor" finalists Emblem3, but the boys said no.

Sources close to the K-clan tell TMZ ... Kendall Jenner is obsessed with the Cali boy band and wanted them to play a gig at her recent 17th birthday bash. We're told her famous fam stepped in to help -- Khloe (who is hosting "X") got the band's contact info and Kris made the call. Problem is ... the boys declined.

According to our sources, since Wesley, Drew and Keaton are still competing on the show, they couldn't find the time in between rehearsals to do the party ... though we're told they would have loved to.

Despite the set-back, little Jenner still had a great time ... prolly 'cause her super rich parents turned their pool (ya know, at their giant mansion) ... into her own personal ice-skating rink.