I would just keep reminding them of your pronouns. Maybe you could have a lesson on pronouns. I would find the student that is the "ringleader" and if it is a boy ask him how he would feel if you started calling him "Miss (last name)" if that is not how he identifies. A lot of transphobia starts at home. If parents are transphobic, the student will probably be too. Be assertive, and stand your ground. Your identity is not a joke and students should not be able to disrespect you.

This can be very tough! Maybe having a talk with your students to address their questions about it. Addressing this with a book might be helpful for them.

I'm sorry that your student would do that to you. I would speak to admin and see what they think.

I would have a conversation with them and discuss how it is a serious matter. You are an adult who should be respected in their own classroom and the students will need to learn that. If they don't stop, you might want to bring it to your grade level team or admin and see what they say.