EC2X Auto Reject Call

Hi, I have EC21 module that will be implemented in the M2M application. The application will have nothing to do with call related process so I want to disable/reject all the incoming calls to the module.
I have a different ME that uses AT+GSMBUSY, also I found AT+CLCK=“AI” but it’s under the facility lock function, and not sure if it’s the right one for my need.
What is the best command to be used in this case?
Thank you.

AT+CLCK is valid and implemented through terminals/facilities;At the same time,You can also enable the SIM card data function and disable the Voice function through the carrier or SIM card provider

I have tried the AT+CLCK command but it throwing an error. Did I miss something?

Are you sure you registered for the network?