Yup. Redwolf has a seizure money back guarantee as Sepulcrum just noted. File your appeal with the CBSA anyway, but be prepared to wait a LONG time. At the same time, send a scan / picture of the seizure letter to Redwolf in an email, explaining that they had improperly declared the item as a "receiver" and it got seized. They'll ship you out a replacement at no cost or issue you a refund.
And hey, a year from now you could get lucky and all of a sudden receive your original mechbox in the mail..