Do you mean that someone owes you money but isn’t going to pay?
Usually, unless fraud is involved, this is a matter for civil law not criminal law.
In civil law one person can go to court to complain about another person’s behaviour. The other person can defend him/her self. The court then decides the legal position.
In the UK, if someone does not pay a debt and is found to be at fault the court can order that that person’s assets can be seized and sold to raise money to pay the debt.