my fathers unpaid pensions of more than 20 years

my father has been a hard working public school teacher for more than 30 years. He retired 10 years ago, however only recieved his pensions for 10 years. He is now 75 years old but still has to go up and down trying to claim his pensions. its very sad and unfair that he has worked to hard for the government but has not recieved what is due to him. he is now even partially blind but still has to go up and down trying to get his pension money