App isn't updated and now I can't open it
Hello, for two weeks I haven't been able to open this app called "Calc+". It's a photo vault app where I hid most of my passwords in. Now I can't open it because they didn't update it to the new version of iOS. How can I contact their support if they aren't on the App Store anymore? I can't find the app anywhere. I've tried to search in my purchased apps and can only see my subscription on their app. This is getting really frustrating and I have no clue what to do. Please help me in the comments.
iPhone X, iOS 14