Hi @Gabriela1943 - your experience is typical of an aircover claim. Lots of frustrated hosts with similar scenarios.
Just based off what you shared above one of the missing elements is some sort of receipt from a professional stating condition of the broken appliance, perhaps? You also need proof that it worked or state of the unit prior to this guest - how one does this is difficult to know for each type of claim (video of you doing laundry?). And proof of what the original one cost? which is impossible to have in most cases.
For aircover, like with review disputes, you are dealing with AI (or that is my current impression), so you won't win trying to manage like it is a thinking, common sense human. The main goal is to deny and make you go away, it seems.
So what to do: if you have an option to resubmit, do so but with all the info needed for an aircover resolution. Keep in mind that AIRBNB doesn't seem to view 'replacement' or cost of new as the driver for what is covered. You can also consider a 'shame' campaign and post on AIRBNB social media to get a human response. But you really need to have a sound story here - as you can imagine, there are a lot of false claims and bad hosts that have led to making this impossible for the rest of us.
And the other advice you will also see around here that is a truism: don't rely on aircover! it isn't insurance. So make sure you have insurance for a case like this.
Good luck!