Combined 2 houses into 1. Can they charge me double maintenance?

I have got two flats converted into one in a society.Till now i have been paying maintenance one and half times . but recently they have decided to charge me for two flats and not one. As there are two types of houses ie; 2 bhk and 3 bhk....and they are charging same for both. I am asking them to charge according to sq ft even if i have to pay more i am willing . Where do i stand legally? The society is not registered as yet.