Airtel Sim is not working in United States

I moved to Florida, US for a few months and want my india number to be active. But it is not showing the airtel range on my iphone 10 neither on automatic mode nor by selecting AT&T/T-mobile manually (though it seems latched to these networks by blue check sign but there is no range). I have tried using another android phone too. I reached out to airtel customer care multiple times via email but no useful response as of now.
IR service is ON on my number and I am paying my bill every month without any delay. There is no point to stick on India's best network.

Please help me to make my number +91-8800091833 working asap, for at least incoming SMS.