Exactly. Corporate structures, governance, and regulation have been formulated to treat corporations as "persons".
Well, that "person" lied. Regardless of the specific agency it employed in doing so.
(And, this type of banning and cut-off from data is obviously -- just look at the comments here -- not a one-off scenario. I find it difficult to believe that the consequences, including the customer's lost access to their data, were not thought about by MailChimp, as an organization and by people in their official roles within MailChimp.)
P.S. As I've grown older and observed and thought about things, I've come to see this as a primary role of the corporation or other such entity: To "dilute" responsibility and accountability to the extent that no member -- or, no member who has sufficient influence, who "matters" -- is ever held personally accountable for their actions within and on behalf of the corporation. [Addendum: And, in turn, the corporation is never truly held accountable, because the employees involved "lacked knowledge". Nicely circular, eh? By the way, I don't consider paying a dollar amount that is often a fraction of the gains realized by the behavior, to be "being held accountable".]
I've stopped letting people in such corporate or institutional roles off the hook, just because "they didn't know". Or rather, I've stopped letting the corporations and institutions off the hook because employee X didn't know. All too often, it's set up precisely that way and on purpose.