I think its just the hanger that has broken. They're not cheap, but they cost less than a new frame.
Keep the old bits and reassemble them, and then compare with https://wheelsmfg.com/derailleur-hangers/all-derailleur-hangers.html to find the right one.
You might be able to shortcut the process some by brand, at https://wheelsmfg.com/derailleur-hangers/manufacturers.html
Keep the little bolts too, the replacement may not come with new ones. You can buy the hanger from your Local Bike Shop, or perhaps direct from dealer. The wheels-mfg ones are good quality aftermarket options.
As for why it broke in the first place - this is a deliberately weaker link that is supposed to save the more-expensive derailleur and frame from damage if something is really wrong.
You said the chain "slipped down" which suggests the limit screws did not stop the chain from jumping off the cassette and possibly bound up, tearing the derailleur clean-off.
Check your chain and rear derailleur for damage too -there may be a side-plate sticking out or a twist or even a stiff-link.
On reassembling, ensure the limit screws stop the chain from moving off the cassette in both directions, and then leave them alone while you do indexing.
Good luck !