They are bundled, but you can use a modifier to override. The question is....was the modifier appropriate? You're 'attached' letter is not attached, so it's hard to tell if the use of the -59 is warranted, and it may be that the payer felt it was not. But according to your post, I think you may have unbundled inappropriately. The code 19301 is a partial mastectomy, which you indicate is being done on the right breast and then 19302 which is a partial mastectomy with lymphadenectomy also on the right breast, but a different quadrant. Here's the problem: You can't do a partial mastectomy twice on the same breast. A partial mastectomy on the breast with the lymphadenectomy, is coded with only the 19302, regardless of how many sections of breast you remove on a single side. It's still a partial mastectomy as long as breast tissue remains. The payer, unfortunately, paid the lower charge, which is how they slap you for billing it incorrectly. If I were you, I'd rebill a corrected claim with the 19302 and beg for forgiveness.
You freaked me (us) out with the patient information, we really don't need to know any of that when you query this board, and I sure hope it's not real. Just provide us with the coding details, and usually someone can help.