How do I turn on my hot spot so I can text and call off my iPad

Despite your attempts at various methods, you have yet to explore the crucial step of utilizing the SIM card from your iPhone 12 Pro in alternative devices. This is because the functionality of a Hotspot is contingent upon the carrier rather than the specific device in use.

Please see the pic below to make it clearer that Hotspot is enabled by a Carrier on one SIM and not by the other Carrier in the same iPhone (Dual SIM).

Use these steps first

Restart the iPhone or iPad that provides Personal Hotspot and the other device that needs to connect to Personal Hotspot. Make sure that you have the latest version of iOS. On the iPhone or iPad that provides Personal Hotspot, go to Settings > General > Reset, then tap Reset Network Settings.

If Personal Hotspot is not working on your iPhone or iPad (Wi-Fi

Also, check the following

1. Network coverage and stability
2. Data Balance
3. On your windows (See if WiFi Auto Joins is enabled)
4. Also, check if you have any stronger WiFi signal around your computer.

Ask the Carrier to change the SIM if nothing works.