Mom comes over and takes my children, acceptable?

My mom lives around the corner. She is a control-freak and has always thought she is my kid's mother. We have a newborn and a toddler plus my oldest from a previous marriage. The child she manipulates is my oldest, mostly. We were in the den caring for the baby and my son disobeyed us and called her someway via his iPad. All the sudden, we noticed that she pulled up to our house and my son ran out the door into her car and she took him. He nor she never asked our permission an in fact, we told him he isn't going to her house (dont ask) and to get off the phone. He screamed and threw a fit. I chastised her via text telling her she nor he got permission and I was not allowing her to take my child. She has ignored my texts. Was this acceptable behavior? What can I do?
Added (1). My husband is not his real father and he hates him. My mom has brain washed him into thinking she is his mom and he has to stay with her.
Added (2). we even told her he is not going to her place! Period! End of! Instead, she comes onto my property and takes my child without my permission!
Added (3). Oldest is nearly 9. He also lies and will tell her that we said he can stay over there. We distinctly told him get off the phone, you are not going. He EXPECTS and DEMANDS to visit her every single day. She will tell him "next month I have meetings or am going on a cruise and you better stay with me now". My mom was never married or able to have kids and I was adopted. She is in her late 60s and wants to adopt again or foster.
Added (4). she has a clicker for my garage for emergencies, she constantly opens my garage and lets herself in.

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