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.
I don't know who they are but they just called here at dinnertime and the call display said Private Name. No message left. All signs of a scumbag fraudster, not a recruitment effort for a charity.