Should a law firm be required to correct their own mistakes for free?

My mother died in October 2018. While pursuing a course of action with a lawyer to get her life estate from three names to two, I discovered an error in the deed that a lawyer in that same practice had made 20 years earlier, which decreased the amount of land in the estate. Before that error, the land on the previous deed was correct. I was told by my lawyer that it was not an easy fix, estates had to be re-opened, probates done, etc. They are going to charge me fees to do all this. Since it was the lawyer's mistake, should all this not be handled by them for free? I have looked at the Code of Laws for my state, plus the bar association's rules and regulations, and the topic of correcting lawyers' mistakes couldn't be found. Thank you.