I was charged for my medical health benefits through pay period 02/28/21 to 03/13/21, shouldn't they be active until 03/13/21? ?

I live in Northern California and worked for Dignity Health Medical Foundation. My last day at work was 02/26/21. I thought that my benefits were good until the end of March. Wrong... Yet I thought that because I was still charged my last paycheck for the date 02/28/21 to 03/13/21. Shouldn't it be until 03/13? Yet my medical last day was 03/01 and dental was 02/28?! No one told me anything so I assumed which I shouldn't have, but I thought that if my benefits would expired sooner that they would of sent me a letter. Of course they send out a letter on 03/24/21 which I just received to tell me that my benefits expired on 02/28/21! Is this even legal? Or how can I go about it? Do I have the right for them to extend it until 03/13/21 since they charged me already? Please help because it would help for them to at least extend it until 03/13/21! Thank you!