You write it as 11,500.003
Assuming you mean (eleven thousand-five hundred three) thousandths, that the same as 11503 / 1000 = 11.503 If you actually meant eleven thousand-five hundred AND three thousandths, that would be 11500.003
The way ou would write six thousand two hundred and three hundred eleven hundred thousandths is 6200.311
602,000.311
Eleven and twenty-three thousand, four hundred six hundred-thousandths.
Eleven and twenty-three thousand, four hundred six hundred-thousandths.
Three hundred eleven and three thousand, six hundred eighty-five ten-thousandths.
Eleven and twenty-three thousand, four hundred six hundred-thousandths.
Eleven thousand, four hundred twenty-two and fifty-three thousandths.
Eleven and three thousand, one hundred thirty-two ten-thousandths.
You cannot write it as it appears.
115300
Most people would say, "Eleven point two three four oh six" but you probably want "Eleven and twenty three thousand four hundred six hundred thousandths