You defintitely have a case of weevils. FYI weevil eggs are in most of the cereal products we buy (I know disgusting!). But they usually do not hatch unless the product has been on the shelf for a long time and it got warm.

For me, I would not do business (no matter how convenient) with a store that 1) didn't rotate its product often enough to avoid the weevils hatching and 2) didn't bend over backwards to take care of your situation. At the least they should have checked the product with you and then given you a store coupon (not to be used on oatmeal!) far in excess of value of the oatmeal as a measure of good will.

I would take it back and stand there as the management check the shelf for other buggy products and then insist it all be removed so as not to cause other customers problems. Then I would give them a lesson in good store management etc but then, that's just me!