How do you deal with foster parents who lie all the time to your judge and caseworker?

My foster parents are always lien to my caseworker saying how im such a horrible child and accusing me of doing stupid things. They have accused me for stealing a GPS out of their car on my 14th birthday and said it was because i was being bitchy that day and then they found out i never even touched it. How do you deal with people who are like that? They make me very frustrated and stressed and i need help.