Lincoln Financial continuously offsets my son's LTD benefits. It is upending his already difficult life.

My son was diagnosed with brain cancer in 2013. He is 41 years old. He has had 3 craniotomies. He has been on LTD thru Lincoln Financial since 2014. They required he file for SSDI and was approved Oct 2014. His approval was very rapid as his diagnosis is one of the 88 that falls under their CAP or Compassionate Allowance Program. His diagnosis is terminal. Upon being approved for SSDI, LF required a copy of award and offset his benefits. With both benefits he would get slightly more than he was earning monthly so I do get that. several times a year the require updates and I always listed his sons information. Two weeks ago i received a phone call from his new case manager, informing me his claim had been transferred and now oly reviewable one annually. This was only after they required him to undergo a brutal 4hr neurological psyche eval. with end results stating he could not hold a job. The new case mgr. kept encouraging me that I should contact social security to make sure his son was receiving benefits. I said he might be. After several pushy statements. I said to the claims mgr. “I don’t get it, why are you pushing this?” He informed me that his dependents benefits might be offset as well. This is horrible! That means they will leave my son virtually nothing to live on and we have made plans, arrangements for his living/care expenses. His situation is complicated. His condition does not allow him to tolerate much social interaction, to the point where I have had to make sure his living conditions are quiet and secluded. Offsetting more income will completely upend his life and impact his health. LF knows people don’t out live this type of brain cancer. They know he will not collect into old age. My grandson lives somewhere in MD with his mother. We are not in contact. My son has never claimed him on his taxes. None of the monies if any come to my son. This is a benefit the SSDI pays. How can LF not know if he is getting a benefit and now come back nearly 4 years later and demand it? The case mgr. says the employer is requiring this. Is there anything I can do?