Ask for the money lenders' registration number. If they're not forthcoming, you can report them to the police.
The answer is NO if the police cant/wont do anything.
As the debt is to do with a business dealing gone sour so even the details on if any money was actually taken/used is dodgy and probably nothing official.
Worst thing is that you dont even know who the money is owed to, have you found out which debt collecting company is calling you or is it just some random guy, then it will probably be a TRIAD debt collector.
Maybe, maybe not. I think all we know is that it is a debt.
Anyway, one of my good friends here is Sith Ifrikan and whilst usually a mild mannered guy, if you set him off, he's absolutely terrifying. I wouldn't demand money from a Sith Ifrikan!
Fokken Prawns!
Given the worrying circumstances, I would double your efforts to make contact with your uncle and find out exactly what the situation is. Maybe he is avoiding phone calls but could you send him an email or even a snail mail to get in touch? Or find a way to contact him via your other relatives?