Claim Denied for timely filing

Hi everyone! A year ago I was taken to the ER. it was outpatient and I had to stay the night. All other claims regarding my visit (ambulance, doctor etc.) had been processed and coved by insurance. I have Blue Cross Blue Shield as a provider. Since it was an outpatient stay the benefits claim that it will be covered by insurance. Around december, I checked my claims and it had said that it had been denied (for timely filing). I called up the hospital directly and i think they submitted a duplicate claim which was denied again. I recently noticed the denied claims and the hospital stated that I do not need to worry about it as they have to submit an appeal. I checked in with my insurance and they said something along the same lines as the hospital has not submitted an appeal and haven’t checked back in with insurance and said that i do not need to worry. I cannot attach the claim screenshot here for some reason but it says that the amount charged was $1000+ but I owe $0. I have not received a bill but I cant help but worry about the denied claim. I’m new to the US and don’t have a full grasp of how exactly this works. Am I all covered? Do i need to do something? I’m kind of worried and i hope due to this elongated time span it might backfire on me. it might just be me being anxious but I would really like to know if i should be doing something just in case.