because I clicked my own ads using my cousins device
1st, how do you know it was specifically because of that? Is there a message they sent that implied that?
2nd, if it is true that is the reason, they could know because he was using your WiFi, and accidental clicks are *ok* but if he was doing it multiple times, that raises a red flag and then all they need to do is a quick lookup. Also because those who are relatively newer ad publishers are under much more scrutiny than trusted publishers.
What to take away from this: don't cheat the system or you will feel even more regret for continued actions because of disciplinary actions against your account(s).