Is there any way to claim the entire enrollment was in error (especially since it was) and retroactively cancel the whole thing?
Good question. First of all, we need to understand what is being discussed in this thread. Subject to various qualifications, a "cafeteria plan" is basically a benefit program under which an employee can choose whether a certain amount of compensation will be paid (i) in cash or (ii) in benefits.
26 USC § 125(d)(1)(B). Without expressing any view on the specific situation of the original poster, I can say that, commonly, employers may offer a cafeteria plan under which an employee can choose to receive either (i) cash or (ii) health benefits under a flexible spending arrangement.
According to regulations promulgated by the Secretary of the Treasury under 26 USC § 125(l), one of the conditions for a plan to be a cafeteria plan is that elections under the plan must be
irrevocable except as described in
26 CFR 1.125-4, but even then, revocations are allowed only in accordance with the terms of the cafeteria plan (in other words, the employer doesn't necessarily have to offer all of the exceptions contained in that regulation). Retroactive changes are sometimes allowed, but "error" or "mistake" on the part of the employee is never by itself a basis to revoke a valid election under a cafeteria plan.
Id.
For academic completion, and still without commenting on the specific situation of the original poster, I should also mention that just because the employer advertises its plan as a cafeteria plan yielding tax benefits, that doesn't necessarily mean that it actually is one. The employer's plan might allow elections to be revoked retroactively for any reason. In that case, the employee would be entitled to exercise that right. However, a side effect of the plan allowing that would be that the plan is not a cafeteria plan and so does not yield tax benefits under the provisions relating to cafeteria plans. The only way to determine whether a purported cafeteria plan is actually a cafeteria plan is to read the documents governing the plan.