I think you should wait for the SPCA, sort of. If you don't hear back from them soon, maybe you can contact another agency. It is great that you got the information and contacted someone about it. As long as the dog is contained in a certain area, and not in any immediate danger, let the people trained to assist such dogs take care of him. My only hesitation is that you a said you left a message, and I don't know how often they check those messages.