My mtn sim is not working, but there's network on it

When I click on the app, it says " please turn off your wfi connection and use MTN mobile Internet to access your account " I had no wfi connected and my mtn sim is connected...

I got a new MTN sim and afterwards opted for an eSIM. However I changed my mind over the e-sim because the phone will soon be changed. I was told it will take 24 hours to revert...

I have been roaming my MTN sim since I entered UK two years ago, all of a sudden I lost the network. Why and how do I get it back, please?