"Your online account has been reset"

If your rank and stats have become corrupted, the Call of Duty servers will restore them using a previously stored backup. This means that your rank and stats may not be exactly where they were before the reset occurred.
 
Why ranks and stats get reset

The known reasons for why this could happen include:
Local issue – One guaranteed way to get the rank and stats corruption is through the following method:
Receive a message stating “Cannot Connect to Game Servers”
Go into Local
Once the game reconnects to the servers, it causes the corruption. If this has happened, you can request to have your rank and stats restored by filling out the upcoming form.
Data corruption – There are a variety of reasons for data corruption. If you feel your rank and stats were reset as a result of data corruption, you can request to have your rank and stats restored by filling out the upcoming form.
Bans – If you have violated the Call of Duty: Black Ops II Security & Enforcement Policy, you may be subject to a temporary or permanent ban from the game, which can include having your rank and stats reset. When this happens, your game data will not be restored.
Getting your rank and stats restored
 
Use this form to submit a rank and stats request:

Rank and Stat Reset Request Form

After submitting the form, we will investigate your request and provide a result via email. This is the quickest way to have your rank and stats restored.