Travel Bank refunds have had issues in the past and with the changes in TravelBank operation, it appears UA is seeing the Travel Bank is more of a problem than a benefit.
"TravelBank"- United.com Club & Gift Registry Q&A - No new/renewals as of 23 Apr 2019

You might try the "backdoor" [email protected] email account (if still active) that resolved many TravelBank crediting issues in the past.

Or file a formal refunds request

The DOT complaint is another avenue.