I can't use Call Back because the call forwards to Voice Mail.

Call Back can only be activated while the call is either ringing on a person's phone, or busy. When the called party has forwarded their phone to another number or voicemail, or after it has followed the called party's forward targets, Call Back cannot be activated on that extension. If the called party has activated a forward to Voicemail or another extension, the call goes immediately to where the called party has forwarded their extension.