Amazon - Package Not Delivered

A customer ordered for a WD *TB hard disk and asked for a replacement as the package was not sealed which was false because it was sealed. We checked the customer history and he has been doing this earlier and he takes out the original contents from the hard disk and return only the upper case or covering of the hard disk. We replaced the hard disk and sent him a new one but we have still not been returned the hard disk we gave him in the first place. We reported a violation and warned amazon before hand that he will also file a refund for the replacement we sent and he did so. The hard disk that was sent as a replacement was sent back to us all tampered and fake. We got the claim for the replacement hard disk but we did not even receive the first hard disk. We have been trying to contact amazon and all they do is create cases and tell us to mail them but they do not reply back on mail. We have tried all these ways but no resolution yet. They keep saying without any proof that the hard disk was delivered but we did not accept it or unavailable which is both false. We have incurred alot of losses due to this in the past as well and amazon does not help at all. Really poor service from their side. We are suffering huge losses and a lot of time is wasted due to this.