My dual sim phone was also giving me this error code… I liked your article because it jogged my memory about phone settings. My solution was not on your list. Please add my solution to your article to help others. I do not want any compensation, just interested in helping others.
Please tell your readers to check their date and time settings and set these back to network time. While this may not be common it IS what fixed my problem… Immediately, the MMI codes worked for call forwarding unconditional (CFU). I presume the MMI codes need correct network time but I had set my phone to manual time while trying some privacy settings.
Thank you for this great article!
