Account doesn't work

I bought a 410k+ Account from him , upon receiving the Account I changed the E-Mail and tried to use it , the Account doesnt work and I even had to write Nintendo Support who also couldnt fix the issue.
The Seller blames me for the account not working despite never saying anywhere you arent allowed to change the E-Mail , I offered to change E-mail back and give him the account as it doesnt work. But he refuses and doesnt offer replacement or a refund and wants 50% for the same kind of account again.
Tried to resolve it peacefully but incredibly bummed out :/