Is there any legal way for me to stop this verbal abuse against my ex and his wife?

I receive letters in the mail, frequent text messages telling me how I am a bad mother, that I am disgusting, that all problems they have in their home when my daughter visits them are because I am her mother, that my child would be better off without me and if I really did love her I would let them have her. These texts come from both my ex-husband and his new wife. They almost feed off of each other with the verbal insults and these rants can last for hours. I try not to let it get to me because I know better. I know the truth about how I am as a mother but it becomes very stressful. They will go on about how the stepchildren flourish and thrive in school and activities (neither of these step children are my ex-husband’s children) but because of me being the mother my child finds math difficult in school. I talked with my child's teacher and arranged additional tutoring outside the home. When asked if they would like to take her when she is visiting, they respond with that "this is my mess and I can clean it up myself."