Voltas — 5 star inverter air conditioners

I have recently purchased and installed 2 Voltas 5 star inverter air conditioners in our apartment in Kochi, Kerala State. Both machines have the same issue, namely the temperature is not being controlled to the desired setting. I normally set the temperature in the bedroom at night at 25 Celsius, but the room gets so cold that I ended up with a bad case of bronchitis. The other ac in the dining room has the exact same problem. I am able to measure the actual temperature in the room with a digital thermometer and can easily demonstrate the problem. I suspect this is a design defect in the machine.