The error you've received from Google Play does not seem to be related to App ID, it only mentions that the certificate is not the same and therefore you would not be able to update the existing app. Note that in Icenium you have Run and Publish menus, the Run menu has options to build and run your app in Icenium Simulator or for developer/ad-hoc testing. The Publish menu however is for building your app in Release mode, so that it could be published to Google Play Store. Make sure that the app you're trying to upload is not build via the Run menu, it should be build via Publish.
If the above is correct, then double check the certificates you use to sign the app, it should be the same used to initially sign the app.
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