It is unrealistic to expect something to fit you exactly if you have had no in person fittings. In professional costuming it is common to have at least one, sometimes 2 or 3 fittings to get something right.
All the professional belly dancers I know who are naturally under a D cup pad up a size, so possibly Dahlal was assuming you were going to do the same in which case a C cup would be appropriate.
From what I see from the pictures (and the text was partially cut off) you just need to do some simple adjustments that are a normal part of fitting a costume, even a custom ordered costume.
I'd recommend adding these pads
http://www.joann.com/catalog.jhtml?C...rId=GOBASE CI
Dritz push up style enhancers to the cups.
After doing that you may still need to adjust the shoulder straps and back strap hooks. This is normal. If you don't have sewing experience find a fellow dancer hwo is used to adjusting costumes to help you.
I know people who have received lycra skirts from designers WAAAY too small- this is not OK or normal.
On the "formed" part of costumes (bras and separate belts) is totally normal for the costumer to send something that is in the appropriate size RANGE. It takes many more measurements than just bra size and under bust size to get a bra fitting exactly right and usually a professional costumer to take the measurements correctly. So they send something that will fit with the right adjustments.