Well, if someone had access to your account, that could be a possible issue. I would suggest password changing. Also you may want to try connecting the phone to a computer, via USB cord, and see if you can locate the files through the computer. Perhaps they just are not showing on the device. Another thing to check is that there is nothing else on your device that can be altering things. Bad apps, virus, malware, etc., could cause this. Lastly, you could try data recovery software, however there is no guaranty with that.
Have you tried restarting the phone and seeing if they show then? Also, when you say cloud I am assuming you mean your google account? They will only be there, however, if the phone is set to auto sync files from the phone to the device (and then it sometimes doesn't work). Are you set up for that?