iPhone 7+ update issue

I need your help guys. I can't update my iPhone 7+ whatsoever, how ever hard I try, no matter what effort I went to, nothing, literally nothing works. I always get this message " Unable to Check for Updates".

I tried restarting the phone dozens of times, I tried hard restarting it at least 10 times by now, I tried logging in and out of my iCloud, I tried resetting the phone and using 3 different wifi networks and 2 different SIM cards with different mobile data providers and even went as far as trying 3 different VPNs and even that didn't help, I had 100GB open storage and then went as far as factory resetting the phone twice And using my iMac to try to update it and nothing literally nothing works at all. Something else that should be mentioned here is that I also can't reach the apple update server via browser from this phone and also can't reach the support website but have no problem reaching anything else from my phone. I don't understand what is going on. I have tried everything and I'm at the end of my wits here. I have tried everything any other post or website suggested anywhere. Please help me. Even the iCare centre here in Bangladesh doesn't know what to do. Just told me to buy a new iPhone. Please help me, I can't even open YouTube or messenger without updating...

I'm staying in Bangladesh for work.