So your company accidentally pays you too much. You notice. You email them like a responsible adult. Hey, you gave me an extra three grand. How do I give it back? Silence. 

Or an auto-reply. Because payroll is out of office. Even though money just magically appeared in your account.

This is where you have no option but to realize the agreement you signed when you started isn't there to protect you. That's what (certain places) have laws for. The agreement is there to protect them, from you, and from said laws. Even though you did nothing wrong. You just got overpaid by accident and tried to fix it. Now you are in the negative while they sort it out on their terms and conditions of time.