You became a member before September 1st, 2022. Before said date (which is when you purchased your membership) you can only have 3 lessons a week; after September 1st, however, the prices were increased and the number of lessons were changed to unlimited.
In other words, since you purchased the previous version of gold membership, you get what that version had to offer. To get unlimited lessons, you'd have to purchase the new gold membership which is more expensive.
I'm trying to access lessons from chess.com and it tells me I need a diamond membership. However, I have a gold membership and it says on the membership page that gold has unlimited lessons.