I'm Sick of Spam Calls on my iPhone?

I've had a cell phone with Verizon for a little over three years, and within the past two months I've received 50+ spam calls (calling at least 4 times per day) with different numbers. At first, I just thought to ignore them but that didn't work. I can literally scroll through my call log and every other call is a spam call (or like every number for 8 lines, I don't call that often).

I'm on the Do Not Call list (and have been since I got my phone). I only give my number out to my friends and family, in no way have I EVER put it online anywhere, etc. It's no where online. I don't understand how they got my number, but it's getting really damn annoying. I also tried to block the numbers, but there are over 25 numbers that keep calling me. What do I do? I want them to stop, none of my friends ever get spam calls and I don't understand why I get them.

Added (1). It's not jailbroken.

If you jailbreaked your cell phone I can see how they got it. Your number some how gets into a system if you did that.

A little personal, but if you are late on your bills or have used a fast cash site/borrowed from cash 4 gold establishments. They might direct what you owe to a collection agency and that is a reason for back to back random phone calls. Have you listened to the calls or messages? Or was this during the elections, because non-profit organizations can get your number and spam your phone. (the money that is directly for the candidate, but can surpass the limits on donating to a said candidate or party)

You also can change your number if you're had it for awhile. You'll get less spam right away.eg.new number.

Also in my belief i don't think the do not call list actually works. Might get more spam than before like a friend.

Hope this helped.