1. You are well below the threshold for a refund. Don't use silly and untrue excuses as those are transperent and are the kinds of things covered by your travel insurance.
2. You can keep calling DL, but they do note your PNR and the reality of the old days is over.
3. Do you really want a refund or are you looking to make changes? If the latter, do some homework and figure out what you want and then call DL and ask for it. It's much easier to get free changes than refunds.
One more all won't hurt, but be prepared to move on to changes from there.