Can Aetna use supplemental insurance as an offset? Are they entitled to reimbursement should I be approved by social security diability?

I am UPS employee on disability, I purchased a supplemental insurance which is paid directly from my payroll for over 7 years. Aetna approved my claim but used my supplemental insurance against me as an offset and reduced my claim from 3,000 to 1,000 per month. They claimed my supplement is provided by my employer simply because its taken from my payroll. I was involved in an auto accident and is thereby a no fault injury. My supplement insurance is from another company called Unum. Aetna also informed me that they are also entitled to reimbursement should I be approved by social security disability. Is there anything I can do to appeal this decision in regards to reduced benefits which I feel is totally unfair after paying premiums for so many years for additional insurance to provide for my family should I become disabled?