Samsung S3 — Excessive overheating and battery charging only upto 63%

Address:

South Delhi, Delhi

I bought Samsung S3 about one and half month ago. I noticed that the mobile is getting excessively overheated after only 15 min o[censored]sage. I understand that some heating is normal among smartphones, i have used 3 smartphones before. My last smartphone was Sony Xperia Play. BUT this overheating is abnormal. it heats up so much that it is very hard to hold. My friends have S3 but their phone doesn't heat up like mine. I used an expensive rubber cover for my S3, which got loosed due to the heating of S3. There i realized that i have to go to service center because the problem has accelerated and it might explode if i continue to use it like this. The service center guys kept my phone for 2 days, however they provided me stand by phone on request. After the service i noticed that the heating problem is marginally lowered but the trick the service guys used to achieve this was unethical. they limited my battery full charge to only 63% and the also increased the charging time by 3x. Now when i charge my phone whole night it shows 63% battery life in the morning and within 4 hours it discharges. It takes several hours to charge up again. On top of it heating problem still persist. it might not explode now but still it is overheating unusually. only with the help of cover you can use it for more than 15 min continuously. Please help!!
I don't play games on my phone i just use it for calling, taking pictures and for social networking like Facebook and linked in.
Please help it is a new phone and i don't have money to buy another new phone now.