Another 32DD chiming in...
#1: you look AMAZING. You are so fit and have such a strong, healthy, beautiful body!!!
#2: I'm so sorry you're having so much trouble. Unfortunately, I don't have any suggestions because I bought the same style Athleta tankini top as well as the bikini top, bottoms and swim skirt. It was the one suit that worked best for me when I wanted to be out in the water swimming and snorkeling. It actually stayed in place. Maybe this particular top is defective and worth trying a different one? I've found the Athleta pieces I've purchased have mostly been good quality.
#3: I had a swimsuit revelation a while back. I'm an apple with a poochy tummy that did NOT improve with having a baby. I was convinced that I should cover up my tummy by wearing high waisted swimsuits. One day, on a lark, I tried on a much skimpier suit bottom than I would normally have tried on. And realized that a lower cut actually drew the eye DOWN rather than RIGHT AT the tummy I was trying to cover. Much more flattering. I'm not saying buy a skimpy suit, but what was the "ah-ha" for me was realizing that I shouldn't get caught up in covering up my "trouble spots" which freed me up to try on all kinds of styles I wouldn't normally have tried until I started to figure out what *does* work.
In any case, I think it's obvious that most of us (if not all!) feel your pain with the dreaded swimsuit. I wish you the best in your endeavor and, most of all, want you to remember that it's not your amazing, strong, fabulous body that's the problem. Good luck!!!