Carpet V Biscuit

[lisacat]

I had an infestation in my kitchen of what was 'thought' to be biscuit beetles, the source was removed(a cereal packet behind fridge), and insecticide spray was sprayed all over the house. However these beetles were to be found in other places, not typically near to the source. One or two were upstairs, and others near the washing machine. I hoovered behind the washing machine..nothing was there. Now the spray was said to last for 30 days, and all insects would be killed. It's just been past the 30 days mark and i have noticed about 5 of these beetles in various places. 4 in the kitchen, and one in my living room. I've googled and googled and they just don't seem to fit the biscuit beetle description, they are more like carpet beetles(the varied type) as they have markings on them. What i want to know is how they survived that 30 day spray thing, and also..why would they infest a cereal packet?. I haven't got any pictures as my camera is broken but can someone please give me information on how to eliminate these things once and for all as i've already had two pest control companies around and they charge like crazy!