Why can't I use data or make calls on my phone?

So recently I changed the charging dock on my iPhone 6, because it was no longer charging. This fixed the charging issue, however, since then it seems like the phone is having issues with signal.

It does say the name of the network in the corner as it should, with two or three bars of signal, however,when trying to make phone calls and use 3G, it does not seem to be able to connect to the cellular network. In addition, when I check the signal with an app called "rf monitor", it seems to always be -50db.

WiFi and GPS both seem to work, it seems to be just the Cellular data that is not working after replacing the lightning port.

Does anyone have any suggestions as to what to do to fix this? I've tried all the software fixes I can think of, resetting the network settings, resetting the entire phone, upgrading to the latest operating system and none of these seem to fix the issue, so I'm assuming there must be a hardware issue somewhere which needs fixing, but I do not know what should be replaced if this is the case. Does anybody have any suggestions?