Wifi on my 2 iPhone XR simultaneously stopped working

I am unable to connect to my wifi. once I connect to the network, the symbol in the bar gets disappeared in 2 seconds. I don't know the reason for why it is happening because I have reset the network settings and even updated my phone. both of my iPhone XR are facing the same problem. I am able to use safari and appstore but not WhatsApp and other utilities. and I have no clue how is this happening.