Why can't I connect to VPN on my iPhone 6S?

Hi ! I could use VPN perfectly until last week on my iPhone. Suddenly, after turning off airplane mode one day, I noticed I couldn't connect to my VPN. I thought my VPN app was malfunctioning so I downloaded another VPN app but that failed too. After that, I forcefully restarted my phone which again was futile. I tried almost every VPN app, reset all my settings, cleared space, and did every possible thing but my phone still fails to connect to VPN. I need help with this please, ASAP.

It shows "connecting" for a long time after which it says "VPN not connected"