Some players have found a workaround link but have received a warning and seen their threads shut down by moderators as violating the Rules of Conduct.
BioWare is investigating the situation and has alluded to an issue with certain types of browsers. In the meantime, the CS team has asked those affected customers to contact the company by phone for help cancelling their subscriptions.
BioWare is awarding those players who pay for an additional month of game time by March 19th with a special "Founder" title.
[Thanks to the many, many people who sent us this tip!]
[Update: In a correspondence with us, BioWare has confirmed