Hi i was having similar issues, did you try
*#234#* instead of *#*#234#*#* that worked for me before although my issue now is different.
i was getting an error and work around it by installing
System app remover (root) from play store
then went to apkmanger and click on reinstal Supersu, that bring back the icon
that did not solve my problem of the dialing code not working anymore, but it got me to super su app
hope it helps