Chatty, SMS does not work - could hardware be at fault?

[AntonReiser]

Thank you all for your advice.

This is what I did:

1. Do a factory reset of the modem. It was difficult to find out how it's done, so for those of you how need to reset the Quectel LTE EG25-G Modem, this is the trick:

Code:

sudo mmcli -m 0 --factory-reset=000000

The phone still would not send SMS text messages.

2. Reinstall the Firmware version 02.002.02.002 according to these instructions.
Still would not send SMS text messages.

3. Install FOSS firmware according to these instructions.
Still would not send SMS text messages.

I am out of ideas.

Is there anything left I could try?