How can I block my sim on iPhone

To block your sim, contact your wireless provider.

If you think your Apple ID has been compromised - Apple Support

Device and Data Access when Personal Safety is At Risk

Wireless provider is whoever provides your phone service.

You probably play them a monthly bill.

What does it say when you look at Settings>General>About>Carrier?

You may have to scroll to see the entry for Carrier.

There is also a section called Carrier Lock.

Settings>General>About and scroll down to Carrier Lock.