There’s no way to directly delete your account. And if there is, it’s definitely hidden.
Contacting them doesn’t feel right either, as it redirects to a whole different domain. Anyway, try to file your complaint here: http://customercare.hmhco.com/contactus/contact_us.html – and hope for the best!
Please note that AccountKiller.com is not associated with the business listed on this page. AccountKiller provides easy-to-understand instructions and guides on how to cancel charges and relationships from the list of businesses on our site, we have no affiliation with these businesses.