Why won't she just leave us alone?

Me and my husband Anthony (Tony) have been together 4 years and have 2 kids and one on the way. The only problem we have is his ex wife Merissa. Merissa is so bitter that Tony left her for me that she's trying to make our lives miserable. Me and Tony were dating while he was married to her and before you judge me, I knew he was married, but he was unhappy so I didn't care. He was in a living hell because she was three months pregnant at the time and he did not want a baby with her. He asked her to get an abortion and she said that it was too bad he didn't want the baby but that she was going to have it anyway (stupid I know) so what did she expect would happen? Two months after we met I found out I was pregnant. I asked Tony if he wanted me to have the baby because I would NEVER give birth to a child that me and the father didn't want. It took him a second to say "you're the woman of my dreams and I want you to have my baby" so he left Merissa and we got married 2 weeks before our daughter Erica was born. Merissa was such a b*****. She kept calling me saying I was a home wrecker and that Tony wanted a child and was happy that she was pregnant before I came along and that he would leave me eventually (4 years and counting and he still ain't going nowhere). Merissa is such a dumb *** that Tony offered her money during the divorce and she refused to take it (yeah that was smart) saying "I'm rather die than take a penny from you" now she and her 3 year old Chloe are living in a homeless shelter because she can't afford to take Tony to court for child support and her family won't help her because they always hated Tony so she cut them out of her life after they got together (idiot). Tony questioned if Chloe was even his so he got a DNA test last year to make sure she was his daughter. Merissa says all she wants is for Tony to be a good father since she knows he's a great father to Erica and Anthony Jr., but Tony has told her that he doesn't want anything to do with Chloe and he doesn't feel a connection to her at all. Then the psycho b**** calls me and says "how would you're kids like it if they knew you were keeping their sister away from them" but Chloe is NOT MY PROBLEM, she's Tony's and if he doesn't want to deal with her then oh well. I want Merissa and her child out of our lives so how can I get rid of them for good? We're moving next month to another state and we're not going to tell them, but I'm afraid Merissa will find us......