You cannot use discussion boards to indicate a problem with a specific seller.
"Feedback" is how buyers let the world know about an unresolved problem with a seller. Unfortunately, it must be posted within 60 days of the transaction date.
As far as getting your money back, if you paid with a credit card through PayPal, call your credit card issuer at the tool free number on your monthly statement and ask for a "chargeback due to non-receipt". Most banks will agree to a chargeback within 60/90 of the charge.