Asking for Maintenance before physically handing over the flat

The builder issues me a possession letter in Mar'17 that I can get physical possession in one month but failed to give physical possession. I waited for 1 and half year for them to complete and handover the flat to me but they failed to do so. Finally I paid the project team for the purchase of all plumbing & sanitary items to bring the flat in some shape and took the flat possession in as is state on sept'18 end. To my surprise the maintenance agency started charging me maintenance from possession letter date and now asking me to pay maintenance for 1 and half year. I approached RWA also but the people who took possession of flat 1 and half year earlier is forcing me to pay the maintenance. I approached the builder CRM team to issue the deferrment letter but they are also not issuing it. Maintenance agency is harassing me daily now to clear the dues they charged before final handover taken for flat. Please suggest what action I can take. They are not allowing me to rent out the flat and creating trouble. Look forward to hear on the issue resolution