Changing Apple ID to an alias that is not listed as an option

I'm wanting to change my Apple ID to one of my aliases. I have figured out where/how to change it, however it comes up with a drop down list of options and seems to only list the first few aliases I have created (have had a couple of name changes). I'm wanting to use my most recently created alias which is not an option. I thought maybe if i deleted some of the previous aliases it might bump the new one up the list, but deleting is also not an option. Have been waiting to chat with someone at apple support for over an hour, wondering if anyone could help me with this please? Many thanks