To change what happens when you dial a number using SIP, you may follow these steps:

-> Login to hoiio web portal.  

-> On the left top corner menu icon, in slide menu click on "SIP" app 

-> Click on "Compliance" Tab.

From there you can see this settings and change what happens when you make an outgoing call with SIP:

It is suggested to configure default action as Ask me to do when number is blocked or Terminate the call when number is blocked.