When did you last have a sim card from us, have you recently migrated over to our new sim?
is this the command that you have tried to use so far?
If you’ve had a new SIM since December 2017
To extend the ring time to 30 seconds, first enter this code into your phone: **61*+447458333222*11*30#. Next, press the call or answer key - your phone will do the rest.
You can alter this to ring for 5, 10, 15, 20 or 25 seconds by replacing **30# with your choice of seconds. E.g. enter **15# if you want it to ring for 15 seconds. The most you can extend it to is 30 seconds.