2012 ford galaxy manual jumps out of first gear?

hi my 2012 6 speed manual galaxy drives fine in all other gears apart from first gear.when in first gear it jumps to neutral with grinding noise of gear cogs,at first it was 1 in 10 times and now it does it probably 6 imes out of ten,even when i keep it pushed forward in first gear with my hand it still some times does jump out of first gear with a nasty push back on my rist i mean it really hearts.i have stopped driving the car as im a mini cab driver and cant risk more damage to thegear box.pls help as im unable to work.i spoke to the local garage and they think its the syncromesh any ideas pls.thanks