Unfortunately it's not a bannable offence as such, it could technically come under "griefing" but since the screenshots don't show what you might have been doing with the tower, I can't make an informed decision about whether or not they were destroying it to be pillocks or if they were just trying to play themselves and you were buggering it up.
If what jacouille says is true, you can't expect people to not take an interest in things like this. Without trying to sound like a parent telling his kids to share, you're on a public server so you can't expect to suddenly command a section of it. Also, people usually take a better response to being asked nicely so if you did start insulting them straight away, that probably didn't help.
Anyway, as I say, not bannable under these circumstances, if they did it without provocation then it might be a different story.
Have fun,
Tenne.
