Did you connect the small black coax antenna cable that's attached to the charging port? I believe that's the wifi antenna, but you haven't specified which service you aren't able to use on it. Also, if you have attached said cable, is the connector on the board still completely attached? You may have dislodged the solder points if you ripped it off half-hazardly.
Other than that, I have seen only one time before when the antenna at the top left of the board came undone for no good reason. You'll have to the the entire board out to see if it's attached, but it's worth a shot if nothing else works.
One more dumb question, you haven't put it in the microwave recently, have you? I'm not trying to be a dumbass by asking that either. I had someone come to my store with reception issues on a 6S and we, eventually, figured out the him putting it in the microwave caused all of his issues.