Yes, there are documented cases of tubal ligation failing. But, it usually occurs within the first year after the procedure. It also depends upon what type of procedure was done.
The type where just a band is placed around the fallopian tubes, is the type that failed the most. If the tubes were cut, the chances of failing goes down. But, even here, if the end of the fallopian tube is patent (widely open) and an egg manages to travel across the pelvic region, entering the tube, pregnancy can occur.
The procedure which has the lowest chance of failing, is the one where the tubes are tied, cut, and cauterized. Cauterization entails burning the end of the tube connected to the uterus, so that the scar tissue totally occludes (closes) the opening.
After 11 years, it is very doubtful that your ligation would fail. I have not seen any documented cases that far out from surgery. But, if you are concerned, speak with your GYN doctor. Sometimes, an ultrasound can be done, but not in all cases. I don't think any one would go to a hysterosalpingogram just to check.
But, again, if you are worried, speak to your doctor.