This is a question that is not for us to answer for you. You cannot let the silence convince you of one thing or another. If you confirm it, that is one thing but to break up "thinking it is someone else" might be a mistake. There might be another explanation since the whole prison-thing is about isolation. They might have phone privileges suspended, or he might not have funds to call, or maybe he thinks you are with someone else. We would just caution you to make 100% sure before taking a step that you cannot reverse. You might start by writing him and telling him your feelings.