Why does Bluetooth turn on automatically on my iPhone?

Bluetooth protocol I mean function turn on after a while. I turned off at that function surprised me a lot of time. I don’t use it so I thought function that provides connection should respect my decision. It’s my first iPhone, I choose smallest one and regret. phone with Bluetooth on or dial someone, talk live his own life won’t fits me. How can I get a refund and send it back?

[Re-Titled by Moderator]