For $1000 they should have taken "professional" diagnosis procedures to ask you about plants and such. Any emergency room would ask such investigational questions! Bring up how easily the diagnosis was made from a simple phone call. I would offer them $500 now, conditional upon the account being paid in full and GET IT IN WRITING. I assume they did do dental work so they did provide some services of value, even though it was not critical to do so. Paying nothing will be much more difficult and might cost you more in the long run in time, frustration, and even money....