Unreasonable Rent Charged for Solar Heater

I have installed a solar water heater on common terrace of the bldg. after obtaining permission from the society. In permission letter MC mentioned that they may charge rent up to Rs 1000/= p.m. When I told the Secretary that it was too much on the higher side , he told me that it has been arbitrarily fixed and final amount would be decided in the next AGM . IN the AGM I asked for the basis of such a high charge but was told that the same was discussed in details in MC meeting and cannot be discussed here. By devious means he got the amount approved in AGM. While I paid the amount under protest , I repetedly asked Chairman and the Secretary to let me know the basis for the rent to which they replied that it has been approved in the AGM and we cannot do anyting now . The charge of Rs 1000/=p.m. fo 8'x5' of terrace area (open to sky) works out to Rs 25/= per sq. ft. per month. Kindly comment on this and advise what course of action is open to me now . Regards ,