It’s mainly caused by the credentials have been remembered by Credential Manager. You should remove the credentials for xxx.visualstudio.com which have been stored in 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.