So I know on ours we have it @ 6 I think (do you have a thermometer you can put in it that will show what the internal temp is?). And at 6 it is -10 degrees in our chest freezer. When we only had it @ 4 it was barely at 0. So it probably wouldn't hurt to turn your dial up. Ours is a GE model.
And you could try just leaving it in longer (if you're able to) like a week (if you have like a deep freeze with some space). I've seen ants survive our freezer if we put the bag in there overnight (just a few like you said) but the longer we left it in it pretty much guaranteed none were alive...
Any time we've ever had weevels or ants get in the feed (or come with the feed)(we haven't had a mite issue ever) we always would put the bags in the deep freeze overnight like @Kiki said. Only thing with doing this is the moisture it puts in the feed (it's prob already got some in there...