how to stop an old (no longer used) splash ID app charge recurring on my personal credit card.

at least 4 years ago, i downloaded and used Splash ID password keeper for about 2 years... i no longer use the app, have deleted it from my devices. my credit card was just hit for $19.99 and after reading the terms and conditions, I still can't figure out how to stop it. i have long since forgotten the login password which exacerbates this issue. i don't believe this is an apple pay issue.