They love it. They tore it to shreds. Now they’re scratching slivers of wood or carboard off. You don’t want to spend the cash for another one yet. – Repair it!
If they’ve ripped the carpet off, get out a screwdriver and prize off the rest of the carpet on the section – they’re normally attached with staples hidden in the nap of the carpet.
Figure out how much carpet you need and go to a carpet liquidator shop, or store that sells odds and ends of carpets. For a few bucks you can buy enough to fix the ripped parts.
Trim it to size; then staple it on.
These days a lot of cheaper cat-trees have cardboard tubes for the legs, rather than wood. But you can still staple new carpet to those. If you don’t have a construction stapler use brads or adhesive.