Help! Brother in crisis and in arrears

my brother (25m) was living in a supported living due to him being disabled. he was paying a direct debit through a company and in the last 4 months this company messed up his direct debit and he's in arrears. not once did they contact either him or the family to say he's in arrears until we've decided to take him out of the shared living due to his mental health declining due to living there.
we signed him up to get housing benefits before we even knew he was in arrears because he no longer had any savings and his hours from work were cut back and we hear NOTHING from who deals with the housing benefits. the company that my brother living under said to us "if the problem was our fault he wouldn't have to pay" then the other day we recieved a letter from them admitting that it was their fault and my brother still needs to pay them back. mind you this is over £4000 my brother has to pay them back.
we need advice on what to do