How do I delete an app from the I cloud

I have a Net 10 International dial-or application on my I phone 6s. What it does is dial a long distance access number and then link to the contacts and dials same,. The app I have has the wrong access number. I spoke to Net 10 they said I have to delete the app and then download the new app. Each time I delete by pressing on the app until it starts flashing, press the X ,and it is gone. I have waited several days and downloaded the new app only to have the old one come back. Net 10 advises I am not totally removing the old app and I am just reloading.

Apple Store could not help