Hello, Johnnyvan447. Thank you for posting to the Apple Support Communities. We understand that you are seeing a message to contact your carrier for support with enabling the Personal Hotspot feature of your iPhone. We’re happy to help you get Personal Hotspot working again now that you have updated to iOS 15.
A message like this may show if you need to confirm with your carrier that your current wireless plan supports Personal Hotspot. We would suggest contacting your carrier in this situation to find out about any potential account changes that may be needed.
We can also suggest several troubleshooting steps to complete on your device. The following Apple Support article explains which steps to try first if you are noticing that Personal Hotspot is not working as expected:
If Personal Hotspot is not working on your iPhone or iPad (Wi-Fi + Cellular) - Apple Support
We hope that the information in our reply here provides you with a good direction to getting Personal Hotspot online and enabled again. Please let us know if we can help answer any other questions about this feature.
Cheers!