Company disability, social security and cmpany pension

I have been receiving social security since Dec 2009. My monthly rate was reduced by an amount payable by the company’s underwriter of long-term disability. I signed a document in Aug 2009 that I realized payment would be reduced IF another disability source of income was received. . I applied for my company pension in November 2012. I just received a demand to repay because of this document. Since I am NOT receiving additional disability payments, I do not understand this demand. What they are suggesting would be like Social Security refusing payment due to my pension.