Who do I ask about SNP's?

I have been enrolled in a medicare advantage plan for the past year, and just got a letter in the mail today stating that the cost of my plan is going to be higher next year, and that my Rx's will be $250 more per month than I paid last year. Now that open enrollment is ended, I don't know what to do. I am disabled and can't pay the difference. We have social security, but I live alone with my son. Q: for SNP or other help, do I have to include his portion of our ss income or just my own? The insurance company asked me how much our total income was, and I gave them the total amount, then they told me I was ineligible for extra help through the government. How do I get an application for the special needs program?