Samsung A510F Network Registration Issues: SIM Card & Software Update Attempts

Hello everyone.
Samsung A510F came to me. The phone reads the SIM card, seems to catch the range, but the connection cannot be made, the error "Not registered in the network" appears and sometimes when the SIM card is pulled out, the phone still shows that it has a network.
What has been done?
Swap SIM cards - no result,
Factory reset - no result,
Erase the phone, upload a new updated software via Smart Switch - no result
I disassembled my phone - no signs of water, correct voltage on the 1.8V C5121 capacitor
What's next? Anyone have any ideas?

Base imei to 3310. If your phone is with Plus / T-mobile then it can be blocked for not paying installments.

But does it make sense since IMEI is functional? I checked the internet on several pages and it agrees

Imei may be functional but the operator blocks paying for them. Do as the colleague wrote above, it will be all clear ...