This fix seems a little lackluster. It would seem more upstanding to honor the agreement they had made, and collected money for: i.e. let the 71 users continue the delivery-fee-free plan (with no minimum) for the end of the term.
They were caught having made a mistake: unilaterally changing the terms of a renewing contract without written notice.
The bare minimum they can do is to offer a refund.
Mistake or no mistake, if their goal is to "always try to go the extra mile," they are failing to do so here.
The fact that Instacart is a tiny startup has no bearing on whether they should honor their agreements.
Allowing the customers who weren't aware to retrospectively cancel and also keep any value of the service they already used seems fair.
I think I misunderstood that the first time, or just plain missed it. I'd be okay with it as long as what I quoted above means what I think it means.
The post specifically says it.