I do not know granite needs extra care until I was told several times by different people. It is not a surprise that you do not know. I think you can talk to them to see if you can pay only partial damage. If they do not agree, you probably can take them to small claim court. (Treat it as a learning experience.)
Is it granite tile or slab? Tile should be cheaper and could replace individual pieces. For slab, they have to replace the whole piece. On the other hand, even with the stain, are they going to replace the whole piece? Is $1200 for replacing the whole piece?