How can I WiFi tether my WiFi internet (connected to my phone)?
As soon as I try to turn on WiFi tethering, it turns off my WiFi and tries to tether the mobile data.
You can't do that. WiFi Tethering on Android is designed to make your device a hotspot (providing WiFi access) and using the internet connection from mobile (3G /LTE /4G /whatever).
in principle, it is possible. Your mobile will then act as a WiFi repeater. As mobile phones are designed to establish only one WiFi connection at a time, the solutions require some tinkering and are said to be not very stable.
Kind regards.