2014 Holden Barina won't select reverse

Based purely on your symptoms, a broken clutch is the most likely cause. When a clutch loses the ability to fully disengage the engine from the transmission (through either wear or damage) the gears can become very difficult to select. Sometimes they will engage with a crunch, at other times you may not be able to select them at all.

This is a different problem to a worn clutch which has lost its clamping ability and is slipping, but the ultimate fix is the same: A new clutch assembly.