No reverse does not engage?

So this transmission is a dual clutch so the reverse is controlled by the shift actuator which fail often on these cars. But can I ask if the reverse indicator is on when you have the transmission in reverse? If not, the transmission range sensor can be bad but if it does light up I would replace the shift actuators, they replace them in pairs. Here is what they look like. I would run the codes as well, this can help you may have a:

P0902 / P090C - Clutch actuator circuit
P07A5 - Clutch stuck
P2831-P2836 - Shift fork issues

https://www.youtube.com/watch?v=LBCpCWEFnTg

Check out the images (below). Please let us know what happens.