Thanks everyone for your reply. Really appreciate. Quick update on the thread. Spirit Customer Support did respond to my ticket after a few days. They did try to keep me as a member by offering either to add 5K miles to my account, or a $35 future travel voucher with no restriction that is valid for a whole year. After I turned off the offer, they did agree to cancel my membership and refund the membership renewal fee as a one time curtesy (why one-time curtesy? It was not my fault!). Given this whole process takes days, if you want to cancel your Spirit $9 club membership to avoid automatic renewal, plan ahead for it -- give it at least 10 days.

This is really bad customer experience; it hurts the brand reputation and credibility. Spirit is a good company; they could be more thoughtful about this. Number one, they shouldn't false advertise the online membership canceling feature since it doesn't work. Number two, they actually can implement the "persuade customer to stay with new offers feature" into the online cancelation experience. That way they could achieve the same goal but with good customer experience and less support cost.