Maintenance charge

When our society was under construction I have combined two flats of one room kitchen each for my convenience. The door of the second flat was closed by bricks and now I am using only one door. The flat was registered as one unit and only one light meter is fitted for this flat. After around two years the cooperative housing society was formed and the builder handed over the building to cooperative society. Everything went well for next few years. Now the Secretary/Chairman is asking for maintenance charge for two flats. My question is whether I have to pay this charge for two flat which actually do not exist and it is made as one unit during phase of construction, registered as one unit, having one electricity connection and no objection was raised initially. Please guide.