Vauxhall Insignia gearbox/clutch

Gearbox or clutch does not seem to be engaging whilst driving under 30mph, there is repetitive noise outside the car when there are problems with the gearbox followed by a really strong burning smell from outside the car. Also when I approach a junction or go down a gradient at 30-40mph and apply the brake it doesn’t drop down the gears and the engine is racing. My Insignia is a 2.0 litre Elite Auto and the gear transmission has been the worst Auto gearbox I have had, it is as though the gearbox doesn’t know what gear it should be in. My car is in a Vauxhall dealership at the moment and they are saying they can’t replicate the problem or find any faults on the electronic fault tracer so telling me nothing is wrong.