Huawei — gave honor 9 lite for servicing, they are charging for defective motherboard which is under warranty

Address:

Hyderabad, Telangana, 500084

I purchased honor 9 lite from flipkart on july first week 2018. Few days later mobile started getting blank display and working one/two days and again blank display. Same hppened for one week.
I gave mobile to service center at ameerpet, hyderabad. Authorised service center. They have taken mobile under warranty and today i got call saying motherboard has problems. Screen has a very minor scratch on the upper surface about a 1cm, its very small scratch which has nothing todo with display problem (Blank display).
Now service center people saying i have to pay 4700 for display also, for very small minor scratch only at upper surface blankness isn;t problem, digitizer isnt effected. But they are charging for small minor crack, the main problem is with motherboard which they told they will claim underwarranty, yet askingme to pay money.