The Department of State recently posted an update regarding changes in nonimmigrant and immigrant application fees. On September 14, 2014, certain fee changes were made. The Department of State notes that fees that decreased on that data are not refundable. If you paid a visa fee prior to September 14 and that fee decreased, you will not receive a refund for the difference.
Visa fees paid before September 14 for fees that increase will be accepted as long as the visa interview takes place prior to December 12, 2014. If your visa interview takes place on or after December 12, you will be required to pay the difference between the old and new fee amounts.