Then log into your account, and change it. If you do not have the login, because lets say you no longer have the mobile that you created the account with, then there is nothing no one can do. Most certainly we cannot, as we are CMM.net and have nothing to do with yahoo.
Always create accounts on a landline workstation, then attach the mobile number after wards. This will allow for more options to recover the account in the event you fail to pay your mobile bill(theft, punishment, whatever!)