Green line on Oppo Find X2 mobile

I have oppo find X2 mobile which is 3 and half years old,  2-3 days back a  green appeared on screen after software update.. there is no physical damage on mobile. I contacted oppo service centre, they created job sheet..now service centre has rejected my claim, they said they will take charges to replace screen. They mentioned about some policy change.. What to do now can somebody help..