Stuck in a Loop for Diagnostic tests.

I have breathing problems and recently visited the Pulmonary Department at a Government Hospital. The doctor prescribed some diagnostic tests, but these tests are not available in the government hospital, so I have to get them done outside.which I Can't afford to pay from my pocket. I approached a charitable trust for help, and they agreed but asked for an expenditure letter from the treating Pulmonary doctor. When I went back to the doctor for the letter, he said that expenditure letters are only given to admitted patients and refused to provide one. Now, the charitable trust says they can’t help without the expenditure letter, and I’m stuck in between. What should I do now? Is there any way to get help from the charitable trust for my diagnostic tests? Or is the doctor lying ? Any advice would be appreciated.