Hello Roman_Nemtsev,
Thank you for reaching out in Apple Support Communities. To troubleshoot the cellular service on your iPhone, we suggest to turn the cellular data off and on in Settings > Cellular > Cellular Data. From there, let's test and see if you're able to use the cellular data on your iPhone.
In addition, you'll want to restart your iPhone as it can help resolve unexpected behavior. Here's how:
1. Press and hold either volume button and the side button until the power-off slider appears.

2. Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.
3. To turn your device back on, press and hold the side button (on the right side of your iPhone) until you see the Apple logo.
These steps are outlined in this helpful article: Restart your iPhone - Apple Support
If you continue to experience the same behavior, please follow the remaining steps within this article as it can help resolve your issue: If you see No Service, Searching, or SOS on your iPhone or iPad - Apple Support
We look forward to hearing back from you with an update.
Kind regards.