Is there an air brick or slightly damp exterior wall?
I had dozens of them, I assumed they must have a breeding ground under the floorboards or something. I got some woodlice killer powder off Amazon and put it along the edge of the floor/skirting boards where they seemed to congregated. I’ve lost count of the number of corpses I was hoovering up daily after that. I still get the odd corpse, despite hoovering up all the powder, so there must be some that got down the crevice that is still finishing them off, but I hardly see them anymore.