If you think too hard about Doctor Who continuity it all falls apart
The Doctor destroyed Gallifrey (he says at some point that it "burned"), but being Gallifrey, and its inhabitants being Time Lords, there are clearly creative ways for them to get around it. Remember, The Doctor destroyed the Daleks at the same time, and they keep returning too. With Doctor Who, the rules serve the plot, not the other way around, so if they decide something would be interesting... they just do it, and explain it away with some "timey-wimey"-ness.
As for the person who spoke to Wilf (short for Wilfred), there's no answer to that.