Filing form 1041

Taxpayer had irrevocable trust since 2014. She was alive and she passed away May-27-2024. at this time we requested (as a trustee) EIN from IRS. letter tells me  that we did not  file form 1041 since 2014. I thought we need to file 1041 after taxpayer passed away.. Tax payer was filing form 1040 since 2014. Need help

Thanks

Sammy