You know that's a scam as VISA and MC aren't even in the business of credit lending anymore (in the United States) and haven't been since VISA broke away from Bank of America! They're payment processors, primarily. Only in certain markets (all outside the United States) do they issue revolving lines of credit directly.
Here's a better clue: Visa, Inc., and MasterCard, Inc. (a.k.a.: MasterCard WorldWide), are separate companies, like CitiBank and Wells Fargo.
These people are getting to be really annoying!
Ask them what bank they represent? If they name one, you should call the bank on another phone and ask to speak with that person and tell them what number they're calling from. I bet if the banks get involved, the Feds will put a stop to this madness!