I can understand how losing your second voicemail would be frustrating, before you got the chance to listen to it.
When you are listening to your voicemail, you would only need to press 7 once, to delete only the message you are currently listening to.
As an alternative we also offer visual voicemail on eligible devices. This is a feature that allows you to listen to and read messages without dialing into your voicemail service, so you can quickly scan and respond to urgent messages. With this feature you will still have the ability to access your voicemail by pressing and holding 1 on your device.