Earlier quoted context omitted.
To follow up a bit: I got my citizenship. Then I was approved for Medicare. Then I applied for Medicate part C and D with the healthcare provider Humana. Humana initially approved my application but then sent me a letter saying my part C and D was DENIED the reason being: "Illegally present in US". I have never been in the USA illegally but always had a valid visa until I got my citizenship. So where did Humana come…
This isn't really an immigration question so I would recommend that you speak with a benefits lawyer but it's always a good practice when something like this happens to submit FOIA requests with the appropriate agencies to try to find out what's going on.
It's more an issue with benefits than immigration like you say, but I just assumed I was treated badly because I was an immigrant, so immigrants beware.
Also I wanted to play nice I thought if I caused some trouble for them they would definitely treat me even worse. Immigrants don't have a similar feeling about their "rights", and what they can do, as perhaps native-born Americans have.