Why is there no mobile network connection?

My phone stopped charging and even after trying every single cable, it would not work. Eventually the phone died and I decided to replace replace the charging port since I have a background in computer science and am quite knowledgeable on hardware and pcs.

The whole repair went smoothly, until I turned it back on and put it in my SIM card. Even after trying all the select my own mobile network options, and going to different locations, and making sure that my SIM card works on other devices, (it did), I was not able to connect to connect to any mobile networks. When I choose the select my mobile network from a list, entries do show up on the list, but even after waiting it never seems to actually connect. After this, I replaced the antenna, thinking that I must have damaged it during the repair, bring the repair, but it still hasn't been working. Once I thought that it could have something to do with the do with the new charging port board that I put in, I put in my old board just to make sure that the antenna works on it. Somehow the charging is working on the old board now and even with all combinations of boards and antennas, nothing seems to be working.

What am I missing? How can I get this to work.