I have a problem with my Samsung Galaxy Note9 and its VoLTE feature.
VoLTE itself works fine 'cept for one thing... it won't work properly with my carrier.
My phone comes from UK, it's unlocked and dual SIM.
I am using it in Mexico with the carrier Telcel and AT&T.
The problem is that all of the carries in Mexico that support VoLTE will work fine with the VoLTE feature except for my main carrier, Telcel.
I can make and receive calls from anyone using VoLTE with all the other carriers but Telcel.
When I enable it for Telcel, it enables but when calls come in, they ring for 1 or 2 secs and then disconnect. On the caller's end it acts like if I had rejected the call. For me, the call appears missed in the call history.
It temporarily fixes if I disable and re-enable VoLTE for that SIM card but eventually happens again. (Note this is happening in any of the 2 SIM card slots).
I've tried to enable the VoLTE settings using USSD codes, restarting the phone to the factory settings and even registering the IMEI with my carrier and replacing the SIM card, and this keeps happening, and as I mentioned above, it only happens with this specific carrier, no matter if I use other SIM cards from the same provider.
I cannot load the Telcel firmware because for my model number it won't be available.