I have now received a sleeve - thanks WGTicon.
Jeffdos: The offer was for non-Legend Callaways. These were the balls I received: http://www.wgt.com/proshop/product.aspx?name=3_Pack_of_Callaway_Tour_iz_Vapor_Balls_L39&i=60e73eed-c628-4a0e-b794-a93ad56171a6&b=0f94e638-b489-4220-92d6-33b0af97ff0e&c=Balls
The explanation to me was that I bought credits after the offer had expired, by a day. I can accept that, however, my response to that was that I bought credits only a minute or two after seeing the free sleeve promotion pop-up, so either there was a glitch and the pop up was showing after the expiry of the promotion, or perhaps my time zone messed with it. Either way, I did and still do feel justified in inquiring.
Perhaps, as a suggestion for the future, WGT could have a "WGT promotions" link, where, in one click, a player can check in on the current promotions and know for sure whether buying credits will result in a free sleeve of balls, or double credits by using Amex, for example.
Cheers all, happy golfing!