If you have a physical extension line which you you have configured to be transferred back to a main line number on the 'Busy' or 'No answer' options then this rule can be over-written if you have applied a 'Follow Me' rule on your line.
What this means is that if a 'Follow Me' rule has been set up on your line then it will over-ride the line configuration where you would expect your line to be diverted back to a main line number for the 'busy' or 'no answer' options - instead of diverting back your line will ring and will go to your voicemail.
Please contact us our Support Desk so that we can restore the line configuration settings.