Can u get pregnant on ESSURE?

I'm 36 & have 6 amazing children. 4 yrs ago I went in to get a Tubal Ligation done but due to complications with anesthesia when I lay down flat they refused to do it. So the alternative was to do the ESSURE which is Coils that they implant in your tubes & because it's a foreign object your body basically creates scar tissue around it which closes off your tubes so sperm doesn't get in. But I've heard from multiple people that you can still get pregnant with the ESSURE. I have had to go into the hospital for testing, a few surgeries, etc & every time I go they take a pregnancy test. I tell them that I've had the ESSURE implanted for 4 years now & it's a permanent birth control & they told me that there's always a chance I could still get pregnant. Does anyone know if this is true?