Desperate Need To Save Our Dad

My dad was diagnosed with stage 4 rectal cancer on March 3rd 2017. Since then, he only had a few visits for chemo until Texas oncology denied him help for any treatment because my parents don't qualify for help and only have Medicare. They haven't been able to qualify for multiple insurance companies as well. They only get social security once a month and of course that's used for any other bills to pay with hardly anything left over. They have to pay $6000.00 to get my dad back on treatment through Texas oncology to get the help he needs. Anything to help my dad would be appreciated.