Notify billing via e-mail when current client's company name is updated?

In the photo below you see my company name is "The Core Training, Inc". If that changes, I want to bill to get an email about it.

I already created two process definition's that allow billing to be notified when the billing street address and last name changes. And I created a workflow that will email billing if a contact e-mail address changes. If I had to guess-  company name isn't an available choice as it is a related field?

Is there a workaround for this? I've been working on it for almost 5 days now and I just can't figure this one out.

(For reference, many companies pay for their employees to be on our training programs. If a client switches to a different company, billing needs to know so they don't continue to charge the client's old company their continued training)