I need to delete an existing iCloud account that was set up on my phone using a previous Apple ID. Since the I've reset both my Apple ID and password (lost my iPad) I cannot delete the iCloud account from my phone because it is still under the old id

I have an old iCloud account on my phone.

This account was set up using an old Apple ID and password.

Since then I've changed both id and password.

In order to delete the existing (old) iCloud account from my phone I need to provide the old password from the old and defunct account.

I don't remember that password.

I've tried resetting it through the support network but to no avail.

I need to delete the old account in order to set up a new one.

Any thoughts?