I had a similar experience - the first CM didn't really understand how to deal with my week as it spanned the two discounted periods. Had a much more knowledgeable CM this afternoon. Although the room I wanted (Poly GV CL) was not available with this discount, I was able to get a
AAA discount applied to my last five nights (saved me about $400 - the 20% offer would have saved about $650, so it's better than nothing!). She had to split the week into two separate reservations as well, but said she'd make a note to keep us in the same room for the whole week. She also said to keep calling back to see if rooms opened up under the 20% discount - she said they are constantly changing/updating discounts.
Keep trying and good luck!!