Help: Blackberry Classic working only on 2G ( india)

Hi All, i got a blackberry classic device last month thru ebay. Device works fine but then i got an Airtel sim since post doing some cross check came to know that Jio sims wont work. The Airtel sim is working but only on 2G and the internet doesn’t work. The moment i switch it to 4G or 3G, the network goes away and phone starts showing emergency calls. Anyone else who uses Blackberry BB10 device who can clarify since the phone is 4G , the internet should work. Wifi works fine. TIA