Motiva implant 265cc Demi , post op cup size is only A? why is that ?

You are still early in the healing process and what you are seeing are not your final results yet. At one month you are still experiencing some swelling, sharp, shooting pains and tissue tightness. This being said, what you are seeing are temporary and will improve as your body heals in the next few months. At the first month, you might also experience temporary asymmetry between the breasts, due to the different swelling rates of each breast. One may heal faster than the other, thus the asymmetry. The breast implants are still yet to settle into the breast pockets made by your surgeon. Give your body time to heal. It usually takes around 6 months to fully heal and only by then will you be able to see your final results.

Cup sizes differ enormously depending on which shop you visit. A given breast volume could for example measure 32FF in one shop but 38B in another (these are called sister sizes) - this does not meant that you are not larger or smaller than you expected in cup size, just that you have chosen a given shop for your bra and this is what is measured.  If you look larger than that is the outcome, not the 'cup' value. It is all to do with your chest size or bandwidth and then the breast volume measured according to the bandwidth.