Before you call K2 back, you should do your research regarding dimensions (internal and external) of both suitcases.

I assume that your damaged case is an old model but internet works wonder. The wheels can make a difference but not 4 inches, and the size extendable handle should not really matter.

If the external dimensions of your old suitcase (without expander) roughly match that of the brand new suitcase, then I would advise you to keep it.
If they obviously don't but a significant percentage, then argue to get a larger one free of charge.