society act related

a person is having 2 flat in a society.flat no. 101 & 102. he is having only 1 agreement for sale for the both flats. society is asking him to pay double maintenance as he is tye owner of two flats. but he is not paying because he is saying i have only 1 agreement for sale. so i will pay maintenance for 1 flat only. what is the actual rule ?? under which provision and under which section he should pay double maintenance as he is the owner of 2 flat though there is only 1 agreement for both flats ?