My iPhone 5c keeps on rebooting and won't stop because I was sent some effective power text .

Try to reset your device. This won't delete your data stored on the phone.

Press and hold the Sleep/Wake button

• Press and hold on the Home button
• Keep holding both buttons until the display turns off and back on with Apple logo on it.

Alternatively, you may go to Settings - General - Reset - Reset All Settings

Also see these articles(this first one offers possible solution):http://www.macrumors.com/2015/05/26/ios-bug-crashing-iphones-with-text-message/

http://www.theguardian.com/technology/2015/may/27/iphone-crash-bug-text-imessage -ios

Apple specialists are aware of this issue. Hope they will find the solution soon.

You are welcome. Try possible solutions from the first article