Why doesn't the phone ring?

Question

Mobile devices

What could be the reason for the problem that calls come only from smartphones.
If the phone is "old" (not a smartphone), then there is no call, sometimes it just beeps and that's it.
On the other side of the line, they say that I am busy and the call is dropped.
Phone Xiaome Redmi 5A, put SIM cards from different operators - does not help.
The phone is a year old, the problem started about 4 months ago (maybe it always was, I just didn’t notice), at first I thought that it was in those phones, it turned out to be a problem in my device.

Answer 1

The firmware change helped, Android 7.1.2 Stable was installed, I installed the official firmware with version 8.1.0 Develop - the problem was solved.
On 7.1.2, I just didn’t do it, but the problem reappeared.

Answer 2

Try to go to settings - - -> mobile network - - > network type - - > change to any other
Enter in phone dialing (password - 0000):
Ban all outgoing calls to Xiaomi Redmi 5 3/32GB Gold
Activate - **33* password#
Deactivate - #33*password#
Check status - *#33#
Ban all calls to Xiaomi Redmi 5 3/32GB Gold
Activate - **330*password#
Deactivate - #330*password#
Check status - *#330#
Ban all outgoing international calls to Xiaomi Redmi 5 3/32GB Gold
Activate - **331*password#
Deactivate - #331*password#
Check status - *#331#
Bar all outgoing calls to Xiaomi Redmi 5 3/32GB Gold
Activate - **333*password#
Deactivate - #333*password#
Check status - *#333#
Deny all incoming calls to Xiaomi Redmi 5 3/32GB Gold
Activate - **353*password#
Deactivate - #353*password#
Check status - *#353#
Deny all incoming calls when roaming
Activate - **351*password#
Deactivate - #351*password#
Check status - *#351#
https://mobilagid.ru/code/Xiaomi-Redmi-5- 3-32GB Go...