My mum lied and killed my dog?

I jsut got back from adelaide and my mum told me that my dog got out and ran away, he got hit by a car and they buried him. She said it happened on Tuesday last week but my friend said she saw him at my house on Thursday.She thinks that i don't know the truth but i'm 16 and i'm not silly. My mum has a kangaroo and once Bandit bit her on the ankle and mum tried to shoot him. I'm positive my mum killed my dog. What do i do?