Top left only emergency calls, what to do?

On my phone top left is only emergency calls and I can't confirm a call, because there's always "mobile network is not available". I have a Huawei P Smart and I have informed myself, but I still have not found an answer. I put my sim card in and out, switched to flight mode, but then in the left corner comes "no service" and then again "emergency calls only." So what do I have to do so that I can make normal calls again?

Of course, you can't make phone calls in flight mode.

You have to turn off flight mode.

Yes I have 😂 The only problem is that when I turn off the flight mode that there again "emergency calls only" is

Either there are problems with the mobile operator, or your SIM card or cell phone is broken. Have you ever tried the card in another phone?

Yes… That was the sim card from my old cell phone.

Either your mobile network is currently not available (eg radio hole, but then another network) or your sim card is not active.

And how can I activate it?

Eg via the hotline