Those lives are lost Laura, they only tend to get stored shortly on mobile but they are known to disappear after a while. On FB they disappear the next time you log in to play so at least you can keep them for a little bit. 

Not sure that's true because I have had those lives for months. I was up to 59 of them. Just started using them last week. If they are going to randomly take lives away because they are "expiring"they should send a pop n up message.