Airtel — unable to send sms from my airtel sim from redmi a1

Hi,
This is rafeeq ([protected]). I am using redmi a1 dual sim mobile.. I am unable to send any sms from my airtel sim.. I am able to send message from my other sim. I had given my primary contact number as airtel in all my banking and other activities.. So i am unable to send any confirmation messages for any activity.. I am able to send sms from airtel sim from other mobile handset but not from redmi a1 mobile. I had made this complaint on airtel for past 2 months. I had tried with all the message centre numbers they gave. All they say is issue will be sorted out in couple of days.. Then i dont receive any sms or call regarding the complaint.