User name has changed in pinterest by accident

Registration date
Saturday November 12, 2016
Last seen
November 12, 2016
- Nov 12, 2016 at 09:18 PM
I have used pinterest for years and have thousands of pins uploaded.
One day, in setting, I have overypped the user name, and upldated. I found pinterest gave me a new id, then I want to change back in setting, I keyed in my old userid, system prompted the the id has already taken, and rejected my updating. Now if I typed my old id in url, it appeared, but no way to update, If I signed on normally, it gives me a new content and treated as a new account, all old boards disappeared.
Now I have no way to get back all my pins. I worte to pinterest help, they said no way to change back. The best way is to copy my pins one by one to new account.
I think this is system bug in pinterest, userid should not be allowed to change in setting. Like my case, years of history pins can be losted in 1 second. The system seems unstable.