Call Waiting wont stop.

[WRPJAP]

I had call waiting, call forwarding and voicemail cancelled thru Verizon CS however I sometimes have work calls forwarded to my home.  If I am on the phone the forwarded call turns on the call waiting and then goes back to the company voicemail.  It should see the busy signal and go back to voicemail not turn on the call waiting.  If I use *70 b4 each call then the forwarded call gets a busy signal instead of going back to the company voicemail.  How do I turn this call waiting all the way off.