No mobile network_voice service is blocked

hi, i am in usa since from 2015 and i was using my chennai airtel sim here without any issues till last week. And from last week i am not getting any network in my mobile it is saying  could not able to register to the network, when ever i used to select the manual searching option to select the network. And also i am getting the notification saying that " voice service is blocked" i don't know what is happening, i tried to change the mobile device just to make sure the problem is not with device, and i could not see any difference the problem remains same. And i can say my SIM card is in good condition i am saying this because i can read all the contents from my sim card(contacts,message) so i can say the sim card is not damaged, it is fully a network issue from airtel.
Any body have the same issue and any solution for this problem.

i am currently using Moto e4 unlocked phone.

Thanks
Suresh