iMessage on my iPhone 6 won't turn on

Hi guys,

So I recently got a new iPhone 6 and one day when I was texting my mother, she has the iPhone 6 Plus, about some things she asked me to do while she was out my messages turned green instead of being blue. I thought maybe it was a big or something, no big deal right? Well ever since it has turned green I can't get any texts from any iphone users. I went to the setting to try to see what iMessage was doing and it's turned off, but when I try to turn it on it has a message under it saying "Waiting for Activation" and then a couple minutes after a pop-up titled Imessage activation says " An error occurred during activation. Try again." I've tried resetting my phone with the home and powee button, but still it stays the same. If you could help thank you!!!!