The old Classic Runescape was shut down just over a year ago. If you found your game progress saved in RS3, it means your account was ported over from Classic in 2004. This means that, even if Classic was still going, you wouldn't have any game progress saved in there. At the time (2004) players had to notify Jagex if they wanted their account/game progress ported back into Classic.
The two versions currently available are RS3 and OSRS (Old School).
RS3 is the evolved game. Originally RS2, then EoC and now RS3.
OSRS (Old School) is a new game - you probably think this one is 'Classic Runescape' - it isn't. It is based on a 2007 build of RS2 so is the closest you will get to an old style Runescape. It was uploaded to play in 2013. Everybody playing OSRS today has created a character and started training it since the 2013 release.
The same login/password will get you access to both game versions but you create and train a character separately in each game.