Mealy bugs.
Neem is the worst thing you can use on aroids. It makes a waxy buildup on the leaves that eventually is detrimental to the plant.
Mealybugs are very difficult to get rid of. They are very good at hiding and avoiding something like Neem that is meant to smother them. They also get down into the container and hide.
To really eradicate them you need to use a systemic insecticide. One that is taken up by the plant through its roots and through its leaves.
