Can Walgreens bill me the full price for prescriptions I bought months ago if they were billing the wrong insurance?

I have been using Walgreens for my prescriptions for years, but this year had to switch to a new health insurance company. I definitely updated Walgreens with the new info when I filled my first prescription of the year.

I recently was prescribed a monthly medication that Walgreens wanted to charge me over $100 for, so I dug into my prescription benefits.

Long story short, I learned Express Scripts doesn’t partner with Walgreens at all. It is unclear to me if they pay ANY of the cost if I use Walgreens. Of course, Walgreens never said anything like this and every receipt I got from them said “Cost to you after insurance.” It also looks like the full retail cost was approximately double what I was being charged each time.

Looking at the Walgreens website they have three different insurance companies listed for me, one that hasn’t been active for over 6 years. I have no idea which insurance they’ve been billing this year. I definitely gave them the current/correct one and they have definitely been giving me “some” sort of insurance discount.

I’m transferring my prescriptions to Express Scripts now, but I’m worried Walgreens is eventually going to turn around and demand I pay the full retail price for every medication I have picked up this year (which is significant) because THEY billed the wrong insurance and I wasn’t actually covered at all for Walgreens.

Can they do that?