Previous employer never inactivated insurance

Not sure if anyone here might be able to help…

I just had a baby this past December and somehow ALL medical bills only starting from October and on were put through my old insurance and not my current primary insurance. My old insurance should have ended May 2021 since that is when I left my previous employer. I’ve since been with new insurance through my husband.

When I reached out to both insurance providers, I found out that my previous employer never inactivated the insurance through them even though no payments were being made. This has now caused a huge problem as my current insurance is denying every claim since they see old one is still active.

I contacted my previous employer but I’m getting the run around so far. they tried telling me they can only go back 60 days. Am I screwed here? They should fix this and I’m not understanding nor being properly explained to as to why they can’t fix this. Anyone work in insurance who has seen this before?

I’m going to reach out to my previous employer again and my old insurance company, but I’m trying to be informed before I go into a conversation again with them. This has been so stressful