3 Month Old Puppy

Okay, so here's the deal. I have a labrador/ golden retriever/ pittbull mix puppy. I am only 15 and I live with my parents (of course), so I left my dads house and I went to my moms house. The puppy stays at my fathers house. When I was leaving a bunch of my cousins had just gotten there. So while I was at my moms house I got a phone call from my dad saying he was getting rid of the puppy because it had bitten my 12 year old cousin. ...