I suggest that you write a polite letter to the company responsible for your pension payments. Accurately show what their mistake cost you. Then politely ask to be reimbursed.
That may just take care of it. Also, there may be other retirees that were hit with the same problem. The company may already be aware of the problem, and taking care of those who request reimbursement.
It won't hurt to try, and it does create a record of the situation. Good luck.
