What is the name of your state (only U.S. law)? Arizona

Hi, My ex has been receiving SSI for many years. I have tried to receive benefits for our son on his record for years but was not able to because he was on SSi and not SSDi. Last month my ex tells me that SS put him on full disability out of the blue and he will be receiving retroactive pay back from 1995 that is when SS says he should have been receiving SSDi. Ex says he has to pay an over payment to SSi and then he will get the remainder of the money into his account direct deposit.
My question is if they are saying the disability goes back to 1995 will my son get back pay as well? He was born in 1998. Also, his father owes about 28,000 in back support.

I have filled out application to pull on his record and also ssi application for my son as well because he is ADD, behavioral problems, seliacs disease and also Type1 diabetes.

any inforamtion or suggestions about finding this info out would be helpful SS will not tell me anything because of privacy act.