That is why I charge my phone with my non fast charge ori Samsung charger when Im not in a hurry.

Nope... It froms previous Samsung phones. You can buy it off the shelf at Samsung outlets though.

Send back to Samsung Service Centre.

It depends on your location. I dont have any issues with network connectivity though sometimes its one 1 to 2 bars. You have to call Digi to disable VOLTE but Im not sure you can get it done after enabling it. But not all locations have VoLTE network.

Good to note that. Im usually around town areas, so coverage is pretty good. No issue.

Yes, you can improve battery life by a bit by changing the display to FHD but then again, why sacrifice display / performance just to gain some battery life? Its like getting a ferrari but driving it like a grandmother. Different people different choice though. You could try, though I warrant it would not be that much of a difference for you to downgrade.

Try to save the contacts on phone only. There is an option where sim and phone contacts are combined and it could be because of that.