Ask the money back and go any means necessary to achieve it. Otherwise in a future they will treat you like a garbage without respect. It is not bad from your side to ask your money back but it is horrible they don't feel like they should pay back. By now if they do better they should have paid something back already. Otherwise it looks like you rented their daughter. So if she is mad again you tell her you are protecting her reputation by asking money back. And it may go ugly, but if you don't do it your future will be even worse. They should be happy is interest free. Just give them option that if it goes to court it will be with interest calculated and they will also pay for your lawyer and court fee. It should motivate them. If you marry her looks like good idea to have a premarital agreement. But looks like your relationship is over. Is a huge red flag. Next time don't loan money to anyone. It only creates enemies. My own experience. My dispute running as long as 10 years. Court involve. But I suppose you are having faster jurisdictional system. Yea and you will become bad guy of the year. It is not that much money in your case. Maybe just save yourself and walk away. Because if people don't want to return money they come with extreme idea to spoil your name and create troubles you can't even imagine. Every conversation ( sending letters) do through lawyer that you can't be blame for treats and so. Good luck.