MyUS.com Cancel original shipment, repack with valid reason. Valuables missing. Suspect of Theft from insider Sarasato Florida

I have been using MyUS for 2 years. My recent shipment is a nightmare! One of my valuable items has gone missing upon receipt of my parcel.
Firstly they cancelled the original shipment, repacked and sent (Fedex AWB 781006106815 changed to AWB 781010635369) The repacking net weight is less but the box is bigger (showing that less item/weight was in the repackaging) It was shown that the cancellation of shipment and repacking were done by Michael and Brandon. 
I had been asking why repacked the parcel in the first place ( I had never complained about the postage) and no reasonable answer was given. This person named Kathleen had been sending me apologetic emails but could not give me an exact answer why and who initiated the cancellation and repacking.
When I asked them to search their premise again as maybe the item had been left out, they did not bother to check.
I suspect a theft issue here! What should I do?