I can't activate iMessage with my phone number

fynnie wrote:

I changed a service provider and start using their SIM 10am yesterday, which is 24 hours ago now. And iMessage on my iPhone 7Plus cannot be activated with my phone number (it can be activated with my Apple ID which is my email address but I prefer using my phone number for iMessage and Facetime). The phone number is the same as before as I changed a service provider but chose to keep my phone number.

I have turned off iMessage and Facetime and restarted my device multiple times as the Apple website suggests but it didn't work. Please can anybody help? How should I fix this problem? Thank you very much.

Follow all steps here If you get an error when trying to activate iMessage or FaceTime - Apple Support