Unless you specifically approved installing an app, or gave someone physical access to your phone, it's highly unlikely a message blocking app. I guess it's possible parental or business management control apps can do this, but that would mean it's not really your phone.
I suggest registering an account here so you can reply and give us more details about what is going on, which messing app you're using, what app you think is the culprit, phone make and model, etc. I doubt getting to the app manager would fix your problem, but more info helps us help you.