When I first heard:
John 10:27-30
My sheep hear my voice, and I know them, and they follow me: And I give unto them eternal life; and they shall never perish, neither shall any [man] pluck them out of my hand. My Father, which gave [them] me, is greater than all; and no [man] is able to pluck [them] out of my Father's hand. I and [my] Father are one.
I knew what I heard and read was the truth that only a few months prior I had asked God to reveal to me. I knew that what these verses were saying was NOT what I had heard or learned in my nearly sixteen years as a "cradle" Catholic. It was the pure and simple truth of eternal life by grace through faith and the assurance that my Heavenly Father held me in his hands never to be plucked out. I did not leave the Catholic Church because of any other reason than I saw for myself that I had been told a lie all those years and that God would reveal the truth to any who search for him with all their heart.
You left the Church yourself. No one could have plucked you out, in full accordance with John 10:27-30, which, of course, is a Catholic teaching, because it is in the Bible.