Apple India — iphone technical issues

Address: Mumbai City, Maharashtra, 400076

I bought an iphone x from apple store, maple, powai, mumbai. I faced issues regarding software crash and phone hang for which i had given the phone to the store. They just reset the phone and claimed it to be fine and assured that there's no issue with the phone. I again faced issue where the software werent responding every now and then. They again just reset the phone and gave it to me stating that its working fine. When i bought the phone they assured me replacement in case of issues as per apple warranty but now they just keep saying that there technical team checked the phone for 48 hours under observation and the phone is working fine. They also said that they agree that the phone is facing issues but apple technical team isn't agreeing for replacement.
Imei no. [protected]