Apple India — Charging more for the the battery than the actual amount

Address: 560040

I had purchased iphone 5 16gb white colour &exactly after an year sleep/wake button stopped working(manufacturing defect)for which i had got the cell replaced under company's matching serial number matching & then after 3 years now i am not getting good backup once the phone is charged completely, which lasts only for the couple of hours.so had given it to ample, mantri square for diagnosis, for which they have charged 1000/-rs well in advance & said that battery replacement will cost approx 8000/-rs.after diagnosis now they are saying that the battery is consumed, they cannot change the battery, instead whole phone has to be replaced which will cost 24000/-rs. but the thing is any person who is mad will only do the payment where as outside new iphone is availble for 20000/-rs. why will i go for phone replacement, would rather pay & take new cell only which i dont want. i just want the battery replaced for the right amount.so help me out.