@Marcos-And-Victoria0 You aren't alone in running up against Airbnb's abysmal customer service- it happens to guests and hosts alike, and it's shameful.
But as I understand what you have explained here, this property was sold and there are new owners. It's not clear to me if the same property management company that was dealing with it before is still managing for the new owners?
The thing is, Airbnb can't force a host to honor a price, nor can they prevent any user from cancelling a reservation, be it from the guest or host side. There are penalties levied against hosts for cancelling, specifically because it will inconvenience the guest.
I'm not sure what you expected Airbnb to do, exactly, except reimburse you the additional $4000? Are you under the impression that Airbnb owns and runs the rental properties? All they are really, is a listing service.
Don't get me wrong, this was a really bad thing that happened to you and either the previous owners or the prroperty management company bears the responsibility. The new owners could have agreed to honor the original price, but they aren't the ones responsible for cancelling your original booking and just because they bought the place doesn't mean they are being disrespectful by asking a higher price. All they did was buy a property-you can't sell or buy an Airbnb business, because none of it is transferable- they could choose to keep running it as an Airbnb, or not, using the property exclusively for themselves. The way you were screwed around was not their doing.