Ghosting a lender isn’t really the ethical solution, even if the app is behaving badly. If you genuinely owe money, the fair approach is still to communicate and try to resolve or negotiate repayment. However, defaming or harassing you by contacting your phonebook is also unethical and in many places illegal, so you’re justified in protecting yourself like blocking abusive channels, reporting the app, and seeking legal or regulatory help. Ethically, the middle ground is don’t run away from legitimate debt, but also don’t tolerate harassment or illegal pressure. Handle repayment responsibility separately from their misconduct.