How Do i prevent my parents from diging through my cell?

My parents are really pissing me off and ineed help on it. my freindhas been texting me bout what her mom and step dad have been doing and saying to her. and ive beeen helping her but she doesnt want me to tell any1 and she doesnt want any 1 to no but she told me. But this morning my mom found my fone and she went through it. it was lockd but shes making me etell her the code and if i dnt she will take my fone away for a mnth. and thn i say well ill just have my dad bye me 1 she said thn ill take it away. shes just wanting to find out wat my buisness is and my frans is im 13 and they are divorcd and they are fighting for custidy and im bout to walk out of my moms house and call my dad if i have my fone and have hym pick me up. so PLZ PLZ sme1 help me im tierd of it.