We had this problem at home AND at work (and I work in a building that has laboratory animals, so this was a BIG problem). It turned out I was probably the source of the infestation at work! I had bought some protein bars to keep at work -- in aluminum foil sealed pouches no less! -- and somehow the pantry moths got into the protein bars (which I never ate because they were GROSS -- I just figured I'd keep them around in case I got trapped in the building after an earthquake or something). Those larvae can eat through ANYTHING!
Our company mascot is a mouse, and I had all these souvenier BeanieBaby mice in different outfits, which I think were full of rice, because my mice got infested too and had to be tossed. We couldn't spray because of the risk to our lab mice, and so it was a slow cleanup by trapping the moths and destroying all food items stored in our end of the building. It was kinda embarrassing too, being identified as the source of the infestation.
At home it took a long time too -- those buggers got into closed packages of EVERYTHING -- they flattened themselves to get through the "seals" of tuppers and those click-top packages. They got into the sugar AND the salt. All the grains in the house had to be tossed. And the larvae pupated in weird-ass places like in the crown molding near the ceiling. We figured they came into the house with some food product (the protein bars?) and then multiplied in the pantry for a while before we realized what was going on.
Icky, but better than roaches!