If someone owes you money then it's considered to be a civil matter and there's nothing that the police can do for you if someone owes you money and does not pay you.
When someone owes you money and does not pay you then you need to take the person to small claims court which can sometimes cost you more money than what the person owes you.
If the cost of suing the person for the owed money is more than what the person owes you then either continue to try to get the person to pay you or just forget about it.
But if the person owes you a lot of money then taking the person to small claims court to get the money through a lawsuit would be a good idea.
But there's still no guarantee that you will get your money in the lawsuit but the judge may be able to garnish the persons wages to get you the money you're owed.