Alright, the main char system works like this:
You choose a main char ---> all characters you have at that time except for the main get tagged as alts.
Alts can never become main chars again so when you delete your main char your only option is to create a fresh level 1 character to make your new main.
Since you did not have a gen 2 char yet and your deleted main is lower level than your alt I reset the role on the 21 char and you can now make it your main.
Please be aware that this is a one time thing and from now on you will have to use the usual way as described above.
Have fun!