Depending on your 'losing provider' you may not have to cancel the service upon completion of the port. Your best bet to confirm where your number is pointed is simply to call it. (IIRC, CallVantage will disconnect your service automatically. However, once you have confirmed the port has gone through and incoming calls are going directly to your voipo line, you can always call CV customer service and confirm that your account is terminated.)

You can always submit a ticket and ask if they have a port date confirmed yet.