Samsung S5233a Mobile Phone — Parts replaced during service, phone dead

Address:

West Delhi, Delhi

I am using a samsung star S5233A mobile phone. This month there was a problem that just after charging completely the phone battery dropped in 10 minutes only and then it got switched off. Despite charging many times it was the same status. Then I visited the Lakshya Service centre in Rohini Sec-4 for service. The guy there named Pramod said that the service charge Rs 75 is applicable and post examination they will tell me the actual expense and then would only they replace the faulty part. After some days I finally got a chance to speak to the service centre and they said that the motherboard is changed and when I asked the reason of not taking my consent, they said we will cll you back. Now, I got a call in 10 min saying that my phone is ready and there was only a minute problem. They charged me Rs 275 and I collected the phone from the Sec-4 Rohini Centre. There the guy did not have a battery so wanted me to check the phone at home. When I checked it, there was still the same problem. He said if the problem persists, I can visit the Service centre at Shiva market myself.I did that. They checked the phone and gave to me saying now, there will not be any problems but I need to charge the phone overnight as the battery is deep discharged.
When I went back home, the phone never switched on!!!
Again I visited and they said that the motherboard is dead so I need to replace it.
Now, when I asked them that had it been dead, the phone would not have started earlier post service but it was just showing the 'battery drop' problem.
They said we can not helpp it.
I took the number of their MD but that number is incorrect.

Please look into the matter as I have serious concerns of my phone parts being changed and their change of statements every time strengthens my doubt.

Kindly look into the matter and help me.

my number is [protected]