Mother In Law creating fight

Hi, From day 1 of our marriage my mother in law is creating either or disturbance between me and my hubby. As he is the only child of his parents, his mom is very insecured and I dont understand her intention behind doing backbitting and creating fight between me and my hubby. My husband works in Mumbai and I live with my in laws and 3 year old son in Gujarat. He comes every saturday morning to Gujarat and goes back on sunday to mumbai. These days she is so caring and loving, i thought she has changed, but coincidently 2 days back i learned shez backbitting about me to my hubby by saying this that over phone. It coincidently got recorded in my phone and while listening to songs, I heard the recording and learned about it. What kind of action can i take to bring her to track. Please suggest me. She acts so smartly infront of son as if shez very caring. she is very mean and money minded. she is just back of my salary. just wants me to work and earn and give all my earnings to them. I am also single child of my parents, bt am nt able to give them a helping hand also. Please tell me what should I do. My hubby blindly believes his mom's words and is a mumma's boy.