Why do my mobile is getting hot when i charge it?

I own a nokia 5610 Xpressmusic mobile, its jus one yr old. Within one year itseelf i gave the mobile for service in nokia care showroom. On the first time after service there was no clarity of sound while using it in loud speakers. After the second time of service the mobile got really hot when i charge it for more than 20 mins. this happened only after a month after service. Already i have spent 1500 for repairing the while servicing it for the second time bcos the scroll panel got damaged. Donno wat is the pbm now after repairing it for the second time. Can any 1 hlp me wats the pbm with my mobile?