Alias can't be changed when From address is set to it.

I've tried everything on https://mymessages.wireless.att.com/messageOptions.do to delete my alias, and everything I do results in "Alias can't be changed when From address is set to it."

I've tried every combination of From, Alias, "Delete Alias," and Submit and always get "Alias can't be changed when From address is set to it."

If anyone has successfully deleted or changed their alias recently, please tell me how you did it. If you got the same thing, what number did you call to get it deleted/changed?

Thanks!