The technically correct answer to your question is no, you cannot force the lawyer to stop mailing letters directed to your mother at your address. What you describe is not an actionable invasion of privacy. However, a phone call to the lawyer should take care of this problem. If not, a polite letter to the lawyer asking him to stop should definitely yield the desired result. If not, you might consider throwing the letters in the trash without bothering to read them. As best I know, there is no legal remedy available to you here.