Check the four pin connector that plugs into the motor with a multimeter.
There will be three white wires and one brown. Before testing you need to fool the car into thinking the boot is closed or it will not work. Do this by clicking the boot lock inwards twice, your dash screen will tell you if it thinks the boot is open.
The wires are numbered at the connector and you should have the following readings with the wiper switch off:
1- White wire - 12v
2 - White wire - 12v
3 - White wire - 12v
4 - Brown wire - Ground
Then when the switch is on:
1 - 12v
2 - ground
3 - ground
4 - ground
If you are not getting the correct reading on wire 1 then this will be controlled by a fuse in the board next to the steering wheel. It could also be a broken cable.
Wires 2 and 3 are controlled by the two relays. These are located under the steering wheel, accessed by pulling out the folding cubby hole. From memory they have the number 404 on them. They are on top of each other at the bottom right of the relay board.
Wire 4 is a straight forward ground cable.
If your problem is a broken cable it is highly likely to have broken under the rubber conduit as you look at the tailgate from the rear of the car on the left.
Another tip I can give you is that the same relays that control the rear motor also control the windscreen wash motor, if this is working it is not your relays that are causing the problem.