Can they reduce your check if you receive ex husbands retirement when on Social Security Disability?

I am 58 and receiving Social Security Disability, I started to get a small check from ex-husband (per divorce), it’s from his retirement. I understood retirement would not affect my disability check, but now they say I owe them money and they have reduced my SSD check by half, the lady that did the application put down the check as alimony and that my ex died, neither is true, it is his retirement and he is not dead. What do I do now, I cannot live on what they are giving me right now, I lost my home on top of that.