Sims 4 Character Glitch

Are you sure you didn't start a new game by accident ?

How did you create a new character ? They changed the way it works and you now need load the old game and then use the button on the lower right corner to create a new Sim.

You can't create a new one for the same save from the main menu anymore

Try the following

1. Save the new character you created to the library (maybe it's already there)
2. Go back to the main menu and use the load button
3. Load the old save game you made
4. Place the new character from the library to your old save game.