Notice for alterations in flat

Hello. Its been 4 years since possession has been given but no OC as yet. The residents of a particular wing have now formed a registered housing society and are now pressurising the buildet to issue OC and transfer conveyance after repairs and other completion of works and payment of taxes. Just today I received a notice from the builder mentioning that I have made changes in my flat like adding flower beds etc which is delaying OC. I have not made any structural changes in my flat. The changes done by me are - 1. Knocking off a non load bearing wall and making it an open kitchen. 2 adding grills and flower beds which almost all other residents have also done. This is just a pressure tactic used by the builder in my view. I would like to know how should I respond to this letter. For e.g. if the builder is stating delay of OC due to changes in my flat, can I ask him to show me the letter from the concerned authority stating this? What should be by response to safeguard my interests