Hi DigitalDave,
They must have a collection system if they have said they will pick it up for you, twice now. I wouldn't wait for the phone call. I would phone them back up and request to speak to a supervisor and ask them what their returns policy is, and whether they do collect or not - if they collect ask them why they have failed to collect on two occasions now and that you cannot afford to waste anymore time, staying in and waiting for someone who 'might' attend.