No 4G/3G signal, reboot and new sim not helping.

Hello,

New to the community, so I'll try to be as detailed about the problem I'm facing. I have an iPhone 7 Plus that I have had since launch. I've had no problems to date, until now, and despite going through a number of troubleshooting both via internet searches and getting help at a local branch of my mobile phone telephone network provider, I've been unable to find a working solution.

As stated, I own an iPhone 7 Plus. My phone can no longer make use of 3G/4G signal, despite it showing that it's available and occasionally kicks me off of connected WiFi networks, which then require me to turn off WiFi briefly and then turn it back on again. If I don't do this, it will show me connected to any acceptable WiFi networks but be unable to make use of the connection.

Per the 3G/4G issue: I have tried rebooting my phone, wiping the phone entirely, replacing the Sim with the help of my local O2 branch, resetting network settings, changing data roaming on/off, and resetting the Mobile Data Network settings. I've also tried switching Voice & Data to use all of the three different settings: 4G VoLTE On, 4G VoLTE Off, and 3G.

Nothing appears to be helping and despite moving to different areas to see if it is just this one city that I'm having signal problems in, it appears to be occurring in every location I try.

Note: This started around the time I upgraded to iOS 13 and while I am not blaming the software upgrade, I wanted to include as much information necessary.

Any help you can provide would be greatly appreciated and if I can provide further info, please just let me know.

Kind regards