Unable to make or receive calls xiaomi redmi note 9 pro

Hello,
Yes, it could be the SIM card, which may be old and therefore the phone has trouble recognizing it.
Solution:
--Either change the SIM card (this does not imply changing your number, as a SIM card is just a code)

--Or opt for eSIM, which is a virtual SIM card, so no issues of this kind (personally, I don't know much about how it works, so I can't help you much)

--Or there may be a setting that is blocking the call:
---often, Do Not Disturb mode cuts off all calls, vibrations, etc.
---It could also be due to a setting that blocks anonymous calls.
---There is also a setting that can interfere, which is an option that blocks certain numbers. Potentially harmful, or otherwise

In fact, the problem is quite vague, so there are many ways to resolve it.

PS: most of these settings can be found in the "phone" app.

Hello...
I think this brand should be avoided. I had a Redmi Note 8 (after 3 returns for repair, the problem was not resolved, proximity sensor) my contacts couldn’t hear me during calls, both receiving and making calls, while I could still hear them... eventually, after taking it back to the seller... I bought a Redmi Note 9 Pro and had the same issues, plus the messaging app opens immediately... so I'm going to request a return and a refund... no more Xiaomi for me.

Hello...
Thank you for the information, I called my supplier and replaced the SIM card... my wife has a Redmi 8... same supplier... no issues, so for me the phone is the cause... and on the forums, there are discussions about the problems encountered with the Xiaomi series 9... anyway, for me, the refund process is underway.
Best regards