Please find the errors.
You returned 2 BlockBuster DVDs on Nov.21, 2007. However, you returned DVD "A" in a wrong container and you also the empty container for DVD "B". Actually DVD was missing for DVD "B".
Would you please return the proper belongings immerdiately?
Box would be the normal word used for a container used for DVDs in Britain, container isn't wrong and you should use it if that's the word that you'd normally use.
You could change the sentence to something like "Please immediately return the missing container and DVD 'B'".
Hope this helps.