Can I Believe United Health Care Saying I Got A Letter By Mistake?

Hello! I’m posting to see if I would be able to get some insight into a situation I’m having right now — and keep in mind I’m still a student so I lowkey have no idea what I’m doing and haven’t had encounters with health insurance like this before.

So TLDR: I’m under student insurance and I get a letter saying that I have to refund United Healthcare money because I essentially got a prescription under my insurance at a time I wasn’t covered by them. I have a feeling this was because my school just changed the health care provider they had been using previously. But when I called them to see if I could pay it virtually instead of having to send in a check, the representative said it was a mistake that it got sent out and that I could disregard it. However, when I asked if I could get confirmation of that in writing, whether via email or mail, they said that wasn’t an option.

I have an unsettling feeling and I’m not sure if that’s my anxiety or if I should follow up with someone regarding this. I know there have been a lot of scams and the number I called was the number straight from their website, but I much rather be more safe than sorry. I would love to have anyones insight and reflection! Thank you!