Plan inactive but paid claims – insurance won’t reverse them?

We had a qualifying life event and unenrolled from our health plan and enrolled in another. However, the week after the qualifying life event, but before we submitted the paperwork to unenroll retroactive to the life event, several prescription claims went through the former plan and we picked them up at the pharmacy without telling the pharmacy that the insurance changed (we were tired, new baby).

They were not very big claims (plan paid ~$100 for 3 prescriptions, our copays were ~$20 total). I instructed the old health plan to reverse the claims (since the plan was inactive on those dates) so we could bill the other insurance. They said there’s nothing they can do because it’s a pharmacy claim and the pharmacy has to do it. I escalated to a supervisor, same answer. I sent a written message, same answer. I spoke to the pharmacy, the pharmacy said the insurance has to do it.

Will these claims be reversed? Who will bill me? Should I just forget about it since it’s so little money?

I just don’t want to be responsible for the “before insurance” amount if the claims get reversed.