According to the situation you mentioned, the company has changed its name and corporate legal person. From the perspective of company law, it is a newly established company and has no relationship with the original company. If you want to prove whether the new and old factories belong to the same person, you need to see whether the shareholders of the new and old companies are the same person. If they are the same person, prove that the new and old companies are related, and you can require the new company to pay joint and several liability. But if the shareholders of the new company are completely different from the shareholders of the old company, it can only be said that there is no connection between the new and old companies, unless you have evidence that the shareholders of the new company hold shares on behalf of the boss of the old company.