I have to to reset network setting always in my iphone 5, when i want to use data?

Please tell anyone know what to do, is there's any problem in my phone or in my sim card, i'm using bsnl

Same thing happened in my 5c recently
you know what's reason,
service provider is culprit,
i posted on official fb page of airtel that if you didn't fixed issue i'm going to switch to vodafone
within a day they fixed it,
on forcing that y its happening they ultimately admitted that my internet settings were hanged from airtel
they admitted their fault
nothing to worry call bsnl customer care