I just checked my messages because I had a new one but when I looked I saw that one of the people who's meassges I was saving (for sentimental reasons), wasn't there anymore. Which I'm ticked about! I know I didn't delete it, so since when did they decide to start deleting your private messages? And, what makes them think it's okay to do that? I was saving that for a reason and now I won't get those messages back and I'm upset about it.
From now on, copy and paste your messages you want saved into a document and save it on your computer or screen shot it from your phone. I'm sorry that happened to you. I thought I had saved messages longer than three months before, but perhaps I am mistaken.
If you message GAG, they might be able to give you the content of those messages. There was something of mine that got deleted and I asked them if they could send it back to me, so I could save it somewhere else. They gave me the content. So as long as they have it on some back up somewhere, you might be able to get it back. Hope you get it back.