Why isn't my HTC One M8 accepting call forwarding calls?

[AC Question]

HTC One M8 not accepting call forwarding calls

Hi all

Just wondered if someone could explain why I am not getting any calls through when I have a call forward to me mobile.

Basically at work we have a generic mobile phone and occasionally we need divert/call forward to our personal mobiles.
When I enter my number, my phone doesn't ring but shows a missed call. When I call the work number and it diverts it goes straight to my Voicemail.
I have tested with other members of my team but I am the only one with HTC one M8

I accept calls fine when a call is delivered to my phone number

Thanks in advance