I felt the pain around a month ago with exactly the same issue, unable to change online, and had to call. But then the first call went interrupted during a transfer resulting in only the itinerary being updated in the PNR but not re-ticketed. Ended up calling several times with multiple tries to get it fixed.

It is time-consuming and very painful to talk with some agents over the phone, that you know the rules better than him/her and he/she could not do anything.

We blame DL for furloughing too many skilled and experienced employees at the beginning of the pandemic and could not bring them back now.