Original Android Keystore / Google Play Signing for existing app

We're trying to publish a new Android update for our app, Alice Ivy, but we're unable to sign the APK/AAB because the original keystore doesn't match the credentials we have.

Could you please confirm:

Do you have the original Android keystore used when the app was first published?
If so, can you export it (or provide the necessary signing credentials)?

Our developer has confirmed that the current signing credentials don't match the existing app on Google Play, so we're unable to upload any updates. This issue is currently blocking all Android updates for our live app on Google Play, so we'd really appreciate your guidance on the fastest way to resolve this.

Thanks!