fraud by spark mail - readdle

Hello;

I was using spark mail app but i've noticed that they keep my passwords with 2 way encoded that means any of Readdle can see my mail passwords. (iphone app is Spark by Readdle on the App Store )

so i've removed that app from my mac and iphone and i've mailed them to delete my account from their servers.

They have critical privacy issue and they refuse to delete my mail account which is https://en.wikipedia.org/wiki/General_Data_Protection_Regulation

how can i report this app to apple?

Thanks