Minecraft Email issues

Recently I changed my Minecraft e-mail from my parent's email (its been 8 or so years) to allow for one of my siblings to use that email to create a new Mojang account. After I changed it, I went to set up my sibling's account with my old e-mail but I kept receiving the error message "there already is an e-mail associated with this account". How can I fix/resolve this issue?

-(posting this thread here after 20 mins of no response from the minecraft forums)