Don't unclog the holes, be patient. I suspect the bees put some eggs into the tube then mud then more eggs and more mud. They bees will most likely emerge next spring when things warm up. I am not familiar with the brown bee, but Mason bees (which people will keep in those same type of tubes) here in the US emerge in spring and are active for only a short period (6-8 weeks). The tubes sit idle the rest of the time. Don't despair.
RE: The Weekly Bee