Intex Mobile / Intex Technologies — abnormal working of mobile only after 3 months of purchase

Address:

Nagpur, Maharashtra

I am gajanan from nagpur... I bought mobile handset of intex in month of june..
(Model name - intex aqua supreme plus).
It was working normally until last month.
But after that unknowingly it lost the 4g network and one of my 4g sim stopped working but that sim is working properly in another 4g handsets and only 2g sim are working and also other features are working well for now... That means the problem was in phone and that was told itself by intex service centre when i took the mobile for repairing... Next day they told that it is the problem in motherboard... And it does not come under warranty and also that it will take nearly 5000₹ to repair. I bought this phone from amazon at price 5500... And now they are saying that it will take so high amount to repair. What kind of service is this?
Company says that 1 year warranty is their and when taken to repair they do this..!!!
This is the worst service i have ever scene in my life..!!!
Please solve this issue and help me to get out of this worst situation...
Hope so you will look into this matter!!