transmission

I would first check the linkage have someone shift thru the all gears while you watch and make sure the linkage on the transmission is moving like it should.If thats all good you could just have a worn out clutch.

ok we've done that and whats weird is there is plenty of clutch pedal there and it didnt give any warning or weird noised before going. it just stopped.

You can have a hard pressure wise clutch pedal and still have a worn out clutch disc they can very suddenly also without warning or you may not have noticed it was going.The clutch master and slave cylinder is only used to release the clutch nothing to do with engaging it when you let up on the clutch pedal it just lets the clutch go back to it's resting state which is engaged.