OP is certainly due a refund, even if on an UP fare.

It is also reasonable for DL to toss in a few token miles as compensation for the involuntary downgrade.

Considering that many people consider unilaterally ending a conversation to be rude, it is hard to know what this aspect of the issue really means.If DL complaints are like what we hear on this board, about 80% of such will have this as a tag line. I would suspect DL ignore it unless specifics are involved.