But you've only tried one form of communication. If you consider the email address? Is it generic? Or a named individual whom you know still works there? A large company with generic addresses like info@ can quite easily misplace your email. The person administering the mailbox may forward it to the wrong person who may be on holiday anyway etc etc.
Why not ring them up? Even if it's just to ask who the best person to email is?
Don't take it personally - yes, they do want your business (probably) but, the larger the organisation, the more important it is to get the right person.
Cheers
Whirls