I bought Premium, but I still see ads
Sometimes, due to a network glitch, the subscription status doesn't update in time.
How to fix it:
Open Converter → Settings → Premium → Restore.

If that didn't help, check your subscription status:
iOS Settings → your name → Subscriptions → Converter.
If there's no subscription or the date is red, the charge to your card most likely failed.
Unfortunately, I don't have direct access to subscription payments and can't help resolve this issue.
In this case, please contact Apple Support: https://support.apple.com/billing