Addition of external passage into flat.

Dear Advocate, Recently we have bought a flat in Malad. While buying the flat society was not made. We had been informed that by the seller and broker that since our is the corner flat the passage in front of our flat can be included into the flat after the transfer is done. However no written document regarding the same was provided. We obtained NOC from the builder regarding transfer of the flat. Now the flat is owned by us. Electricity bill is also transferred on our name. Builder also mentioned that we can incorporate the passage into our house without any hassle. Last month we started with furnishing of our house and also extended the flat by shifting our door into the passage. The extension in no way obstructs the neighbors door, view etc. In our building there are 8 corner flats and each one has extended their area. In fact everyone has extended it till the neighbors door we however left 1 and 1/2 feet space between the two flats. Now the owner of the adjacent flat has made a complaint against us in the society which was formed just last week. We have already invested in the extension and now redoing it will cost a lot. Can you suggest us what can be done in such a situation. I understand that this may be classified as encroachment or illegal but if it is illegal for us it should be same for all the corner flats. Can only one person make us change our actions. Please advice.