What should I do about forced marriage renouncement and threats?

Sir, I had a love marriage in a registered temple. After one month of marriage, the girl changed and went back to her home. Later, her father and brother forced me to write on a plain paper that I no longer have any relationship with their daughter, and they do not accept this marriage. Now, their daughter is ready to marry someone else. All this is happening without a divorce. They are threatening to send all the marriage witnesses to jail. They are not ready to accept the marriage, so they are not willing to give a divorce. What should I do? Please guide me properly.