I was told my son could not be claimed on taxes as a dependent since he was receiving SSI for Cancer...

My question to everyone in cyber land is... My mother claimed my son, without my knowledge, on her taxes from 2003 until 2010 as a dependent the entire time WE were receiving SSI benefits for him because he was diagnosed with Leukemia in 2003 at age 5. Fast forward to 2010 and we are closing his SSI out since he is "Cured" and they tell me I have to repay all of the $58K back to them that we received but will not tell me why. Now mind you, during the entire process I complied with EVERY THING SSI asked as his treatment was paid for through SSI medi-cal and I wouldn't risk losing his insurance. When I was working I sent in check stubs as we didn't receive the cash benefits all the time, filled out the hundreds of papers they sent, did the phone interviews, etc. etc. etc.

I asked around and everyone seems to think it is because someone might have claimed him on their taxes. Some more digging I learn my Mother, who did not have permission much less my knowledge, claimed my son on her taxes the entire time I received SSI. Could this be the reason SSI is coming after us now?

Anyone ever been in a similar/same situation... any advice/input would be greatly appreciated. My sons cancer is gone, now we just start to have a "normal cancer free life" and then this happens...

We live in Southern California if that matters to the response. My son was diagnosed at age 5 in 2003 and was under Dr. care until June of 2010 when he got the "All Clear" and was no longer "disabled".