Iphone X has blank lock screen

I started to have the issue of a blank lock screen right after i downloaded an "HD wall paper & lock screen" app. It was well rated and seemed legitimate. But when i opened the app i discovered that it would charge me $8/weekly. So i immediately deleted the app, and that is when this blank lock screen began to occur. I restart my phone and it helps for a few hours, but the screen goes blank again to where i only see the wall paper.