Sailnetīs demise, this suggests...
Will, assuming that - at this moment - you have successfully stopped payment from your credit card vendor, then I would present your question to them. Eventually, they will need to resolve your despute re: the charge and so it will be their opinion of your actions taken that will matter to you.
At the least, I would consider sending a registered-return receipt requested letter to Sailnet, explaining your dilemma and asking for directions on the return of their (incorrect) merchandise. Until they respond appropriately, Iīd hold onto the merchandise.
IMO they deserve no consideration when shipping the wrong item and then not offering customer service to resolve such errors.