How to include an additional key to the email to avoid duplicate contacts

Summary:

We need to include in the form some rule, configuration or customization to avoid duplicate contacts.

Content (required):

From a form we have the possibility to update or create new contacts in the Eloqua database. However, we are having the following use case which causes us to have duplicate contacts. For example:

A contact is registered with an email: empresa@correo1.com and with a document number: 1234567

That same contact can re-enter a form and complete the following information: corporacion@correo2.com and with the same document number: 1234567

Eloqua understands that this is a new contact, but in reality it is the same contact because it has the same document number.