In your MyBT profile there is an option to add a "recovery" email address and phone number to your account for instances such as this.
It might not allow you to add it now because your account is locked but could be worth a try.
Failing that you will need to call BT 0330.1234.150 and ask them to reset your password. They will require you to answer security questions and if the need to send you a PIN they should be able to either send the PIN to your house phone if you have one or it can be sent to your home address by snail mail.
