BAND account is based on all three personal information 'name, birthday,and mobile phone number.' Therefore, you can't access previous BAND information if you change both device and your mobile phone number. If you want to keep your previous BAND account, please register your NAVER ID before you change the device and mobile phone number. There is a procedure to connect your BAND account with NAVER ID as following steps: [BAND app>Settings> Register NAVER ID]