How can I convince my Mum To Let Me Buy a puppy?

it has been my birthday recently and i have got around $600 (australian) dollars. i went to the shops with friends today and saw a puppy that i realllllllllllllllyyyyyyy wanted to buy. even though i have a dog already i wanted to buy this puppy, so i rang my mum and said no because it would poop all over the house and also when we go on vacations it would be expensive to keep 2 dogs in a dog hotel while we were gone. we once had a puppy earlier a few years ago so we have had 2 dogs once before, but my parents sold him while my dad took me to the shops as a distraction. my mum sold the dog because he kept destroying things and it kept misbehaving etc. how do i convince my mum to let me get one? i even offered to buy the accesories like the collar and leash and bowls etc