Need proof that he performed it wrong*
You would definitely need to have proof that he performed it well. Even with it being properly done there IS still a failure rate, and depending on the ligation done some are more to likely than others.
Same thing happened to a women I know and she sued her doctor
Are you positive he only tied one tube and you have proof? You can definitely try to sue them. You may end up spending more wasted time then wanted, since it could possibly drag out to be a very long process.
My husband had a vasectomy in jan 2001 right after my step daughter was born. 9 years later to the date I ended up pregnany with our daughter without a reversal.. And now i'm expecting again. Sometimes it just happens.. Naturally.. Someone has a plan for you that you're unaware of. Good luck and I hope everything goes great for you.
you should talk to a lawyer about that... they would know better