Regarding iMessage activation

When On the iMessage this message come to pop up " your network provider may charge for SMS message used to activate iMessage.

and later on it says " An error occurred during activation. Try again leter."

I have contacted the network provider it looks like it is not a problem with the network provider.

i have balance in phone. And still iMessage activation is failling. I have tried so many times.

this is an iphone 11 pro

please help me