Why am I paying child support I I am on Disability?

Because that's the law - a certain portion goes to support the child.
Many fathers have to move in with family, take in roommates, and really scrimp to survive on what is left, I know. Who do you want to pay? You can check with Family Court to make sure that you and the mother and child are getting all the other benefits possible, and that they are deducting the correct amount.
Are you able to work part time? You can keep your disability and work up to a certain amount each month.

Because you created those kids, and it's your responsibility to help support them.