You will likely find that this is more easily & profitably handled through your travel insurance.

But, if you do pursue it through WN, leave out all the extraneous detail about who said what and point to the specific damage in question, e.g, the wheels no longer align. Ask to have the bag repaired or replaced.

WN can likely get away with simply writing off the bag and providing you with its fair market value which, depending on its age, might not be that much.