Legality of threatening people to pay?

It depends on where the business is located. In the US no, they shouldn't be doing that. Privacy laws prevent a company from releasing or discussing debt to any other person. In other country's embarrment to make people pay is kind of a rage going on. They was an article in the Wall Street Journal about collectors dressing up in bunny suits and visiting people at their homes and offices to embarr them in front of their coworkers and neighbors. It really depends on the country where the business is located and doing business I would think.