Android Mobile recovery app is specially designed to recover lost data from android device. it could recover kinds of lost data, like text messages, contacts, photos and so on.
If you are not rooted, you can download Recuva to recover files. If you have root, then try android sms recovery. In order to aviod data loss, android transfer can help backup your Android data to computer.
So if you accidentally lost your important files and want to get them back in this situation, no matter internal memory or Internal Storage, you can use a software(android recovery software).
how to retrieve deleted contacts
You need the help of a professional android data transfer tool because the contacts are not accessible directly when your phone is connected to the computer. Also you can use gmail to sync your contatcts. Transfer Contacts from Android Phone to Computer