The cast member at room reservations must have been misinformed. If you have a WDW resort confirmation number, you are eligible to take advantage of the 180 + 10 rule.
Here's the scoop on the 180+10 rule:
Guests staying at Disney-owned resorts can make the meal reservations
for their entire trip
(up to 10 days) on the first day of their 180 day window. So instead of
having to call back multiple times, a Disney resort guest can call at
the 180-day mark to make reservations for not only meals on the first
day of their trip, but also for
meals on the following nine days. In reality this means that Disney
guests who are staying for 10 days can make the reservations for the
last day of their trip 190 days in advance, rather than just 180. This
gives them an advantage in their ability to get reservations for
hard-to-come-by meals.
This advantage really comes into play when trying for hard to get
reservation like Cinderella's Royal Table, which is included in the 180+10 plan. Guest who are staying for longer trips so have less
competition for getting reservations for the end of their stays.
If you are making your dining reservations online, you can begin at
6:00 a.m. If you're making your dining reservations over the phone, the
lines open at 7:00 a.m. at 407-WDW-DINE. Either method works 7 days a
week.
To use the 180 + 10 rule online, you must register on the WDW website and input your RESORT confirmation number into the system. To use the 180 + 10 rule over the phone, you'll need to have your RESORT confirmation number available to give the dining reservation specialist.
Good luck!