billing problem

So I downloaded an app called “Fitplan” and I payed for one month subscription. Then the month ended, and it asked me again, to pay, so I did. A few weeks ago I lost my mastercard and I decided that I don’t need the app anymore, so I ended my subscription and deleted my accountnt and the app. Now here is the problem, Apple is still sending me emails that say “billing problem”. But why is there a billing problem with fitplan, if I don’t even have a subscription/account? I tried again and again to see what is wrong, but No luck. I don’t want to pay for another month, if I don’t use the app.