No internet even when connected to the WiFi or 4G (iPhone)
The 1st thing to do when you are facing a network misbehaviour is to deal with one way of connection at a time.
This is what the genius at the bar should have told you first.

Practically focus on your mobile Internet conectivity first:


turn off Bluetooth;
turn off Wi-Fi.


Test your mobile Internet connectivity in different places.

Then conclude: your problem is on the mobile network side or not.

If your mobile phone network is OK

then analyse your Wi-Fi in the same way:


turn off Bluetooth;
turn off mobile phone network (Mobile Data).


Test your Wi-Fi connectivity in different places.

Then conclude: your problem is on the Wi-Fi network side or not.