Check if the website you are logging in is as below.
제한 적용 일시 :
Would you like to change the mobile phone number all at once?
* Information will be changed once [confirm] is clicked, so please decide carefully.
Now, login
with your Email!
Email registration will become mandatory in the future.
Register your Email in advance and continue using Bithumb conveniently.
Don’t worry if your contact number has changed.
You can change your contact number after registering your Email