Have you tried to "Reset network settings" in the Settings?
Since reset network settings didn't work, it's a hardware issue.
I just had this exact problem after opening my phone up. (it alternated between searching and no service) Here's how i fixed it.
Your gold prong is intact, which is a good sign but there's a chance it's not making contact with the silver bezel that surrounds your pnone.
This was the case with me.
Please note: this procedure IS risky. Please proceed with extreme caution. One wrong move could possibly snap your prong, and this will make matters much worse.
Get a pair of needle-nosed pliers and put them aside for now. Turn your phone off, and open it up. loosen the 2 screws (do not remove screw, and the screw directly under it) just a tiny tiny bit. Not even a quarter of a turn.
Now for the hard part. Take your pliers and VERY VERY GENTLY squeeze the TOP prong and silver bezel together. go slow, take your time and take a few deep breaths beforehand (yes that really helps)
As fine as the prong may seem, it's not making contact with the bezel, which is what grounds the cell reception.
I just did this procedure myself and it worked just fine. i really hope it's the solution for you too.