No Network

I am using Realme 2 Pro mobile and my Airtel india number is 9741800771 and its a prepaid SIM. I came to US 3 months back on work assignment and things were fine. But somehow my phone is not finding any signals and showing no service last two days. I do not want to receive any calls or anything just want to receive messages as enrolled in banking and suppose to get OTPs.
I need the network on priority. Please suggest how to resolve this issue.