What can I do when someone threaten to lodge a fake complaint against me?

Upon both families liking each other, On 26 th June, 2023 my dad, middle man and 2 other member from girl family had a close door discussion with girls parents at their house and started further talks about marriage.. Upon agreeing on, it was written on plain paper that the relation is confirmed and marriage would be planned later after certain months... But on the very other day due to disagreements within our own family, we conveyed to them that we would not be able to go ahead with the marriage... so no such official programs/engagement/ are made. Neither I spoke with girl on phone and nothing of such sort is done.. Now based on the agreement on the plain paper, the girls parents are threatening to file a FIR...pla suggest