good for you for finally getting the cassette off. It's really not supposed to be hard, so it's good to install and remove a couple of times yourself so that you get a feel for it.

If only the skewer was damaged it's bizarre that they want the whole wheel back! If I have the English terminology right, it's hardly a part of the wheel at all, but an interchangeable part like the tire.

Oh well, good luck. If you have a backpack you can ride with a wheel strapped to it without too much trouble.