Why don't my parents let me exercise?

Hi, my parents say no every time I want to join a sports club, go to the pool (to do laps, I love swimming), or even go to the beach (because there’s too many sharks, apparently…)
Anyway, they deny everything, and jogs with my dog aren’t a good idea since we live in a pretty bad neighborhood (luckily moving soon.)
They don’t let me eat healthy, and when I try to go on the exercise bike, my dad says to ‘get off that stupid thing’.
A few weeks ago, maybe even a month, they attacked me because I’m “so overweight”. I got so confused and upset I just ran to my room, crying. I am 13 and a few months old, and I’m about 5–10 kg overweight. I want to lose these kg’s and get in shape, as it’s the school holidays and I really want to join the volleyball or tennis club next year at school. Also, how do I explain to them that I’m mostly interested in tennis? Sorry this is so long, but thanks in advance, and any help is appreciated. Please no rude comments, they are still my parents and I love them, they’re just a little hard-headed at times! So how do I make my parents understand I want to exercise and diet?