Inspiron 15 (1564), out of warranty, spare part warranty period

Hello,

I am afraid but I am really experiencing poor support from the service centers. I really don't know how this works but I have a Inspiron 15 (1564) laptop that I purchased back in 2011. It worked well untill start of 2013. In Jan or Feb, it started giving errors so I consulted a Dell Support Center. They convinced me to replace both bard drive and motherboard and I did. However they gave a 3 months warranty for motherboard and only 1 month warranty for hard disk. The replacement went well. But around 4-5 months after that, the PC started to behave weirdly again (it was in Sept) when my warranty for both replaced components had been over. The laptop started to freeze unexpectedly, OS wouldn't boot etc, etc. Now that I went back to them for diagnosis, they are asking me to replace the motherboard again. They said this will cost me around 12000 INR and that too, they are again providing warranty for it just for 3 months where as if I purchase the same motherboard by my own, I am able to get it at around 7500 INR and with 6 months replaceable warranty. I am not a beginner with laptops and suspect something's fishy here. Either they are fooling me now or there was something wrong with the components they installed during the previous (before about 10 months) repair. Please let me know your views on this. Any information in any form is greatly appreciated. Thanks in advance.