our wireless account has been hijacked

[technodoll]

help! the past two months, our wireless internet account has been hijacked and we're stuck paying the bill, whick is almost DOUBLE of what it's supposed to be! we have a password-protected broadband router at home, but there are apparently apps circulating which can easily crack your code and give hackers free access to your account - i feel so violated

besides changing the password again tonight, what else can we do so this doesn't happen again? if they broke into our account once, they can do it again right? help!