your be filling holes a very long time, if you can fit a "biro pen" in a hole, a mouse will get through easily, your better off sealing the outside first, stop further infestation, then dealing with the mice inside, because a sure as eggs are eggs, you'll have a nest or two inside somewhere, also look at "food" as if you take that away, your halfway to problem solved,
it amazes me the amount of people that complain to me off having mice, yet when you inspect the area, theres things like dog biscuits in sacks in kitchen, food left on worktops, spilled food behind cooker/fridge/microwave, a