Iphone 6 Screen Repair after battery qoute

My Iphone 6 was bought at the beginning of January on Contract.(So still under warranty from MTN side)<br> After my phone being taken in for a BATTERY Repair, that is still under warranty. They charge me R 6000.00 for a new LCD screen without wanting to repair the battery? and then my screen wasn't cracked in the first place. How would you explain this. Following your Contract (MTN) that states i have a warranty on the phone you want to charge me for wanting it fixed? I would like your reply on how this is possible after signing a contract that i have the warranty on the phone.