Hecheng law firm sent a message saying that it would sue me.

Legal analysis: A regular law firm will not send you a text message telling you to sue you, or send a lawyer's letter or sue you directly.

Legal basis: Interpretation of People's Republic of China (PRC) Civil Procedure Law Article 132 If the addressee has an agent ad litem, the people's court may serve it on the addressee or his agent ad litem. If the person to be served entrusts an agent ad litem to collect it, it shall be served by lien when it is served on the agent ad litem.