Diana,
Keep at it. Pay no attention to your father. I sense an agenda underneath his laughter. Your boy friend is right. The more you practice, the better you become and the laughter is irrelevant. Your voice teacher is not in the business of playing games with you. (I say this without knowing who it is but voice teachers have a vested interest in the success of their students.)

When I was in junior high school in California, I was asked not to sing but to mouth the words of the song by the teacher. The irony is that I have been able to make a living as a singer. If you love to do it, you will get better.

Frank Hamilton