identity theft

my sister called and asked for my social security number. She lied about the reason she wanted it and I gave it to her. Later I found out my mother had used it without my knowledge or consent to set me up with a trust fund, which I don't want. I don't want either of them to be allowed to used my social security number for any reason. They have not stolen money out of accounts or anything. I just don't want them sneaking around using my social security number to obtain confidential information about me or whatever else they may do. How can I make them stop?