It seems you would be entitled to a refund. Question, though, accepting the 5K miles from CO -- was that a settlement to the issue?

You may want to PM CO Insider about it. Seems he spends most of his time these days sorting out issues the CS organization can't handle.

If you tell him you don't want the 5K miles, rather the refund originally promised (that you have a screenshot of), and CS was unable to resolve this, he might be able to work something out.

Alternatively, you can dispute with your credit card. Especially since you have documentation to back it. Then it will be CO's problem if your CC charges back the funds to CO.