You did not pay full price for the iPhone 6, which is $749 for 64GB version.

The reduced price for 64 GB version is $299. 

In exchange for you 4S (which was worth much less than $200), you got a iPhone 6 for either free if 16 GB version or $99 if 64 GB version, and a free GB of data for a year.  That is a pretty good deal.  Not seeing how you were wronged.