You can reset things very easily!
First, head on over to http://www.comixology.com/login and choose comiXology Sign-In. From there you'll see a "Forgot your password?" link. Follow those steps and you'll regain access to your account in no time!
If you're not getting password resets sent to your email, it's possible that it's not actually the email connected to your account. Or maybe you had an older email account that you used to sign up. Or maybe you just need to use your Amazon account to sign-in, too. If you still have questions, just email our team and let us know that it's a possibility and we can do some digging. support@comixology.com