If it's Josef, the total debt is $1 Million, which you can help by giving him money little by little or by completing Mario Questline.
If it's an unknown man you meet in the Garage, he's a "Debt Collector from Insurance Company" who threaten you to pay $5,000 each week. However, just go to Josef's Office on Friday and check his safe. Put the safe code 7172 and you'll get his Gun. The next Monday you see the Debt Collector again, use the Gun to scare him off ( or kill him?? ) and he'll be gone for the rest of the game.
