Reject button sends call to voicemail instead of call forwarding

I have my phone setup through my carrier so if I don't answer a call it will forward to my work phone number where my assistant could take the call and then to the work voicemail if no one answers there. Everything works properly if I let it ring through, my phone is turned off or if the line is busy, however if I "reject" or "decline" the call it send to my carrier voicemail instead of forwarding. I was told by carrier tech support that the "reject" button is programmed to send to carrier voicemail and that I would just have to silence and let it ring through. Is there a way to change the way that reject button is programmed within the phone so it will forward to work number if I decline?