Just because a person is born again does not make them “deception proof.”
The Lord would not have warned His disciples to “take heed and be not deceived” if there was no danger that they could be deceived. It does not matter how many things you are or were deceived about. For 25 years, I was deceived about a few things in comparison to what other churchgoers were deceived about. Yet the Holy Spirit did not release me from the deception until He was ready to. He simply stepped in when He chose the time to be right and started unravelling things. Why? Because I began to both doubt and question religious teachings and practices.