Is this legal? Supplemental Security Income?

Ok, my fiance was incarcerated on August 30th, will not get out until October 13th. First problem, he is on Supplemental Security Income (SSI) for his disability. He has been receiving this income since he was 11 years old. He is permanently disabled and was incarcerated for something that his disability caused... (It is a mental disability, mind you) He had an appointment, his first ever review case appointment, and because of his incarceration, and the length of it, they are telling me they are canceling his SSI income, after 20 years!? I understand that his needs are being met, meaning his housing and bills, but what about his needs out here? I mean, how is it legal to cancel his SSI that he's been receiving for over 20 years when his rent still has to be paid for so he doesn't lose his house, and his electricity bill still has to be paid for so he has electricity when he comes home, and he still has a family that lives off of that income every month? Someone please help me... This is the last place I have gone to looking for answers.... Please help...