I don't think it's just for PR purposes, but I understand your concern of an unbounded downside. Even a few free deliveries would be something.
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.