why did I recive a text with a code

Hello @user_isb0yz. Thank you for reaching out on our Community Forum. That code is for 2-step verification to verify your account. Did you request a code to sign in to your online Xfinity account? 

Someone somewhere put your phone number in to receive the code.  They may have done so accidentally by tying in their number wrong and accidentally put in your number.  If it happens once, don't worry about it.  If it starts to happen frequently, then you may have a problem.