How can i stop my twitter hacker accessing my account?

[England]

Ok, basically someone got hold of my twitter password and was able to tweet from my account. I changed all my setting such as password and email, but they are still able to tweet from my account as they are logged in on an apple device and a password is not required to log in as the account stays logged in the whole time, so they are not affected by the password change? i can't revoke the access of the Apple twitter apps for iPhone,iPad and iPod as i have an apple device. This is really annoying me and i would be devestated to have to close my account as i have lots of followers including famous followers. I can't find a way to contact twitter about this? How can i block them from accessing my twitter?