If you have insects inside, they must be reproducing in there. Hopefully, these are just fruit flies that have found some spilled juice or something like that. Clean the fridge thoroughly. You may have to remove panels or fan covers or things like that, if the spill have gone inside the fridge. I would swab it down with dilute bleach.
Place small bowls of apple cider vinegar inside the fridge. They will fly into the vinegar.
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