i want to change my phonenumber at my Account

hello, My name is Kim Seung Hyun, from South korea, and I want to change my mobile number to verify my account as shown in the title. This number is definitely mine, and I was able to verify discord with this number not too long ago. However, after I tried to log in to my friend's laptop, I suddenly got a text message saying that my discord account with different numbers is in use, and authentication is not resolved. This number was definitely mine, and not long ago I was able to authenticate with this number. I wonder what happened. Ask me which account is linked to the number +8201084642915 and what I should do to link my account to my number if it is not an accessible account. Thank you for always trying for the users.