I'm a failed tubal ligation baby; my mom had her tubes tied a few years before I was born.
Nothing is 100% fail proof. They say failure rate is 1% in the first year. It goes up after that. That one percent also doesn't include tubal pregnancies, only viable pregnancies. One well done and respected study showed a 5% failure when they included tubal pregnancies.
If you think you might be pregnant, take a test. If it's positive call and schedule an appointment with a doctor asap. The risk of an ectopic pregnancy after a tubal ligation is around 20%.
I have heard of some woman that have become pregnant after. Is rare but there could be a chance