Root c done about 10 months ago?

I had a root c done about 10 months ago. Now im feeling like its loose and its sore. I can't eat nothing hot or cold. I spent a lot of money and Im already having problems? Since i don't have insurance anymore does the dentist has any obligation like fixing it or checking whats wrong with it? Plus when i got this root c done i called my insurance to make sure everything was ok because i was about to cancel it. So i had it done, my insurance paid $1.5 and applied for care credit and i paid for the other $1.5 Two days later the dentist himself called me saying that the insurance didnt paid for anything And i was responsable for paying that. I told him that they did a brake down on my insurance before the treatment. I said i was going to call the insurance and i never heard a word from this dentist anymore. Its a huge clinic with lots of different docs and i wonder why did he call me and not one of the ladies from the credit dep. So any ideas? Do i have to pay to fix this even if he did a bad job?