What can I do about this?

Hi. Back in January/February I tested positive for COVID and was out for a month. My boss told me to send him proof of my positive result, that he was going to send it to the office. I had nothing to worry about and that I was going to get paid. Times passes by and I get a letter from benefits department that said my benefits because I didn't qualify. I reached out to hr, payroll, benefits etc they all told me, it was due to having missed excessive dates, they didn't know I had COVID. I told the account manager she said to send her proof of my positive test result and that she was going to fix it. It's been a month since then. I have reached out and get no response. I had a co worker who had COVID for a month and his benefits never got removed.