Hi temerkhanov,
We would suggest that you reset your APN settings:
Settings > Mobile network > Access Point Names > Tap three dots on upper right > Reset to default.
If the problem still appears, please show us a screenshot of the error.
Please also show us screenshots:
1) Settings > Mobile network > Access Point Names
2) Settings > Mobile network > Access Point Names > Tap the APN with the dot beside.
Thank you 🙂