Called back and got what appears to be an answering machine saying, "This is for subscribers only. We do not recognize your number." If that is the case, why are they calling? No way for me to leave them a message.
This is a fraud campaign currently active in Canada using a series of Iristel VOIP numbers. The objective is to obtain your credit card number and drain your account.
If you attempt to "opt out" your number will be confirmed as live and added to a suckers list for repeated future calls.