If I were to give the seller the benefit of the doubt then he may have been confused because the wiring loom had separate instructions for all the different models - he may have thought that meant the towbar was compatible across all those models as well.
That's quite possible, I thought the same initially too, before I actually tried to fit the hatch tow bar.
Careful with the "screws" holding those plastic covers under the bumper, you need very light touch so those plastic screws actually come out instead of just spin around. Stubby Philips head screw driver will do you.
First photo is the fit of the harness' own grommet. Second is the LHS (looking from behind the car) of the tow bar, you can just make out some of the plastic cover on the right. Third is the RHS. In the front of the bolt on the left is the bump in the car's "chassis" that makes the hatch towbar useless for the CW. Pic 4 should be self explanatory
If you are good with your hands, you can easily work out how to fit those plastic covers back.
Sorry about the quality of the photos, the little compact cam didn't like the underside of the car. Don't have access to a ramp to take some proper shots.