FOLLOW THESE 7 EASY STEPS:
1. Delete the Snapchat app.
2. Re-download the app.
3. Type in your username and click "forgot password."
4. It will give you the option to reset with email or phone. This will only work with phone, so don't select the email option. (THIS STEP IS VERY IMPORTANT)
5. Create a new password.
6. Log in with the new password.
7. Go back to your old ways.