Next stage if you don't pay the CC is TfL register the debt at the Traffic Enforcement Centre, and send you an Order for Recovery. They will also include the form to submit a Statutory Declaration to TEC.
So don't pay the CC, but wait for the OfR. As you seem to have missed receiving the rejection letter, it will be best, after the CC payment has expired, to contact TEC every 7-10 days to see if the debt has been registered. You can then submit an SD using the form you can download from the TEC website. Alternatively, you can look on the TfL website to see when they have registered the debt. Tick the box on the form for "submitted reps but didn't receive a letter of rejection" No need to put anything in the 'reasons' box.
On the actual form, remember that TfL are the Applicant, not you; you are the Respondent.