You need to submit a Notification of Arrears form online. You can do so by using this link https://share-eu1.hsforms.com/1EbY_LJf6TeuB-p0QmOKPUwfu1pd
Should you need to contact the Arrears Team, you can email them on arrears@rentguarantor.com or call 0207193448 and request to speak to the Arrears Department.