Rights for Penthouse owner

Hello, I am a owner of a penthouse. Since last 5 years I am living in it. My flat is of 1435 sqft. Since then, I was paying Rs 800 for the maintenance purpose...as all the flat owner pays equal amount. Now the society persons wants me to pay Rs 1500 for the maintenance.... Just because my flat sqft area is more than all the other residents and all the rest owners will be paying the same 800. So please help me out, as the society members are harrasing me mentally to pay extra amount. is there any law or rights regarding this.? Thanks in advance