Call Fail

I use to be able to receive calls on my desk phone and desktop/mobile app. All i had to do was turn off the Data VoIP Calling in the phone app to not receive business calls on my cell phone. Now even with the Data VoIP off calls come through, but if I'm on a current call or my personal carrier line on my cell , the current call I'm on will fail and end the call coming in. My Iphone has been doing this since the new IOS back in Sept. Is there anyway to get the app to work like it use to?