Hello @Rap1 and welcome to the community forum
It might have skipped your attention but @MP-FP6 issue was apparently solved by (re)setting APN,
Solution identified!
APN settings. Only restarting them and the phone doesn´t do. They needed to be modified. Weeks of recurring exchange with the network carrier, nothing better.
It seems particularily problematic when the carrier asks for the phone model and hears “Fairphone” and responds “it´s not on my list” + the carrier doesn´t let you access the APN (masked).
It´s total guess work.
Here the links that helped me (Salt/Switzerland) - and thanks @Meaghan - Community angel, for the hint ! …
Perhaps you could try some troubleshooting either following the suggestions here
https://support.fairphone.com/hc/en-us/articles/9498003764113-Troubleshoot-the-mobile-data-connection
or via self-repair portal
https://support.fairphone.com/hc/en-us/articles/29507066461458-How-to-use-the-Fairphone-Repair-Request-Portal
If none of this works and you are unhappy with your device, certainly there is no point of keeping it. There is a market section on the community forum where you can try to resell it.