I may have been hacked


Unlikely.
More likely, you left your browser open on a computer signed in to chess.com and someone you know resigned the games for you.
A joke!?
It is good that you changed your password. However, if you leave your computer or phone running and signed in, the same thing may happen.
/ It seems possible that somebody is upset with you.
/ There is no way to reverse the resignations. In 10 years here, I have never seen it done.


Well, you can write to support. Perhaps the logs will reveal how it was done.
They don't usually monitor forum posts.
To prevent hacking I would recommend using strong hard to crack passwords. You can use tools like password generators and password managers to keep track of your passwords. Here is a couple good ones: