It usually happens when credentials are being remembered by the Credential Manager, first remove the credentials for xxx.visualstudio.com which you might have stored in the Credential Manager.
Such as if the pc’s OS is windows, you can open Credential Manager -> Windows Credentials -> under Generic Credentials -> remove the credentials like git:https://xxx.visualstudio.com.
Then clone again, git will let you input the credential for the repo. After inputing the username(email address) and password which can access the VSTS account, the repo should be cloned successful.
You can learn more about frequently used commands on git commands.