Call waiting Connection problem or invalid MMI code

[perryano]

Hello all, I have got this message when trying to activate call waiting on my EU rom mi9. My network settings are all correct in the APN settings as per the telco's settings. My phone rings and sends sms/mms. My data works fine.

I am unable to activate call waiting, and when I try to do it from the menu I get a Network or SIM card error message.

When I put my sim in another phone it works fine with *43# or menu settings. The other sim in my phone still fails.

I have researched everywhere and can't find any possible solutions. Is anyone else had this problem?

 

[perryano]

So my sim works in other phones but other sims don't work in this phone. I have just wiped my phone to sort another problem which is fixed. It seems each time I wipe I get a new defect