Screen not working

Bought my vivosmart 4 in August 2020. Couple of days ago upper half of the screen went completely black and the following day, the whole screen. The screen literally switched off. Device is still working, measuring steps, HR, running pre-set alarms etc. but completely inoperable. Had to buy a new vivosmart 4, as I didn't want to create a gap in my routine. Unless there's a solution, I would like to get my money back - original, broken device is still under guarantee (I've disposed of the original box and papers, but pretty sure it's at least 12 months of coverage). Thanks