It was because a guy (called newbie) supplied my food factory with fruit and maiz. He probably just wanted me to finish game so we could restart. The year was 2004 so the server had already been going for very long, so there weren't any real competition. I had been mostly idle since for about an hour, and thought I might as well finish the game. A guy called "Jelle" started to claim it was planned and intentional to use two companies for one town. Others then joined him and started to destroy my town.
It would of course never be my intention to get advantages with the help of two companies.
Edit: How long does these bans last anyway?