SOGO,
Sorry for your trauma at the hands of radical IFB clowns. Did they give you any SCRIPTURE? Demand it, gently. I would absolutely refuse to resign and I would force the issue to the floor of the church by making them follow the process of Matt 18 to remove you from membership.
This kind of bullying is not uncommon in my experience. You probably wont win anyway, but you do have the obligation to point out their TOTAL lack of Biblical support for such a position.
In fact, Paul regularly preached in Jewish Synagogues even though he had become a believer and left the Jewish tradition in favor of God's clear leading. Yet, he continually went back to his people to try to win them to Christ, their true Messiah.
Suggest you give them the example of Paul and ask how what you did was different from what He did. He was preaching to the very "denomination" that crucified the Lord Jesus. And of course, then there is Peter...
Did the leaders like what Peter did? No. Read Acts 11. Did the Jewish believers like it that Paul was ministering among the Gentiles? Read Acts 15.
Bottom line, point out their inconsistency to see if it makes any difference. If it does not, they are following man, not God anyway, and you really do not want to be there. Pack your bags and go. But, do not go silently. If the story is as simple as you have presented it, the solution is just as simple. Call the leadership of the church to account on the basis of the Word of God. If they listen, you have converted them from the error of their way. If they are prideful and blow up, take your family and leave. If you need help finding a new church, PM me with your specific location and I will try to help.
Ray