It says you have already linked your Activision ID and signed up on the ladder. Can you refresh the ladder page and verify you are now able to challenge users? Furthermore, if you need to change your Activision ID, please go to the settings page underneath your profile picture in the top right. From there you click on "Link Accounts" and you should see your pre-existing Activision ID linked.
I have the problem too it keeps telling me link but i already did and i o to hit join latter and tells me too put it in again and i do then it says i already have one so i unlinked it and relinked it and still wont work idk how to fix it
When exactly did this issue happen? As far as I know, this issue was fixed around 2-3 weeks ago. You may have to clear your cache.