Getting a parking ticket or a PCN can be frustrating and sometimes they are issued in error.
Appealing a PCN depends on the type of PCN you have received. If it is from the Council, you can lodge an appeal here: https://www.sutton.gov.uk/info/200195/parking/1240/penalty_charge_notices/2. If it is from Transport for London (TfL), you can lodge an appeal here: https://tfl.gov.uk/modes/driving/red-routes/penalty-charge-notices/make-a-representation?intcmp=2234. If either the Council or TfL refuse your appeal, you can escalate it to London Tribunals.
If your PCN is from a private company, you will find details of how to appeal on the notice itself. If they reject the appeal, they should provide you with details of how to appeal to the adjudicator.