Selena Gomez' Parents -- BLINDSIDED By Firing

Selena Gomez's mom claims she got ZERO warning that the singer was axing her as her manager ... until TMZ broke the story.

Selena's mom Mandy Teefey says she and Selena's stepdad sat down with the singer Thursday after TMZ's story ... and asked Selena if she was absolutely sure she wanted to move in a different direction. Selena said yes.

Mandy tells us she thought last month's conversation was just talk ... and she's having a hard time processing the fact that she's no longer Selena's manager.

Selena's mom and stepdad had managed the 21-year-old since her big break at Disney -- but as we reported, Selena told her parents she'd outgrown them and wanted bigger management.