As you are talking about economy class awards, and I note form your profile that you are a Gold FF member, when looking on-line you will be seeing the combination of X (standard economay award class) and T (a paid fare class that is also used for SG and WP member awards).

Perhaps the telephone agent you were speaking with was not award that SG and WP member's economy class awards can come from T fare bucket and was only offering you X availability?