Call Ended calling a specific number on 4G

[Cheeseball]

Hi,

I have a very specific problem.

Number A is a number I've had on BT Mobile for 5+ years.

Number B is a new number on a new SIM that I recently added to my BT Mobile account.

Number A's SIM is in a OnePlus 10 Android phone.

Number B's SIM is in an Easyfone t200 4G LTE feature phone.

I can phone from A to B with no problems.

I cannot call from B to A. I get an immediate "Call Ended" message on device B without any apparent attempt to make the call.

All other numbers that I have tried so far can be dialled from B without any issues.

After some further experimentation I discovered that when I reboot device B and it briefly connects to a 2G or 3G network, it can at that moment call A successfully. As soon as it finds the 4G network, the "Call Ended" error occurs again. If I put SIM B in an Android device it will call A without any problems. 

When I first insert the SIM for number B into device B I get the text message "the terminal cannot be configured remotely"

This is a real shame, as the only number that I really want to dial from B (for a senior citizen) is number A.

The problem seems to be something specific about the combination of A on 4G and device B on 4G.

Does an APN need to be set for VOIP on device B? There doesn't appear to be any way of setting this in the phone's settings. The phone is extremely simple but it does claim to support VOIP/LTE/4G.

Any help or suggestions are welcome.

[ctrlz]

Sounds strange but likely more of a device issue.

APNs will be saved to the phone to allow access to use data on 4g. Normally found within the mobile data settings of the handset. Could try resetting to default as most handsets will re-download correct APNs over the air, if not a quick search on the BT website will give you the settings to enter manually, but I’ve not known incorrect APNs to affect calls over 4g before.

You do also get access to Wi-Fi calling with BT, presuming it’s enabled in your handset settings. No other settings are needed for this feature as it’s enabled at a network level by default and just requires a compatible device.

Have any other people reported issues calling B number?

[Cheeseball]

I've been doing some further experiments.

Just to recap:

A is a BT Mobile SIM in a OnePlus 10 Android phone.

B is a BT Mobile SIM in an Easyfone t200 feature phone (not Android).

B is very limited in terms of settings. There doesn't appear to be a way of setting APN settings.

A can always call B, under any circumstances that I've tried so far.

When B first starts up, it occasionally uses 2G or 3G and under these circumstances B can call A. When this occurs, the message "Outgoing Call Forwarded" appears on B's screen.

As soon as B connects to 4G, and I try to call A from B, the message "Call Ended" appears on B's screen, within half a second. No dialtone, or any other message.

Some further experimentation...

If I switch off A or put A into flight mode, when B calls A, I now get the "Outgoing Call Forwarded" on B which then goes to the voicemail of A.

I have tried an EE SIM in B and the same problem occurs.

I have tried a Vodafone SIM in B and this problem does NOT occur.

I have tried another EE SIM in a different feature phone and this problem occurs when it tries to call A when A is switched on.

My temporary workaround is to put SIM B in an old feature phone that doesn't support 4G. It stays on 2G or 3G. But this isn't a long-term solution as this particular phone is too difficult for the intended user to use.

So the problem isn't just this particular feature phone. It is any feature phone on 4G on BT Mobile or EE calling another Android phone on BT Mobile on 4G where the target phone is switched on.

I don't know what settings to try to change next. I've cancelled all call forwarding settings, but this has had no effect. I've cancelled all call barring (there wasn't any set anyway), but this hasn't helped.

I've tried calling BT on 150 to speak to an engineer but keep getting told that they are currently too busy to speak to me.

I just don't know what to do next.

Edit: When a BT Mobile SIM is first put into B, the phone gets the following text message a few seconds later: "The terminal cannot be configured remotely, please contact Customer support for further assistance". I am adding this just in case this is massively significant. I've still been unable to speak to a customer service representative.