Xamarin iOS - Call Voip Sip

I Have one project in xamarin forms. During the development of push notification for iOS, a problem was encountered with push incoming when the application is closed, as well as accessing notification content when the application is closed, it isn't possible to change data without the local iphone database . After much research the solution of using push via VoIP was found, as well as possible to manipulate push when received. But Apple doesn't release the project for publication because we use VoIP without making any kind of call. I need a VoIP solution, without using paid component, to make a Voip Sip call to Xamarin iOS or a solution for receiving push when the application is closed.