Do not bother communicating with the useless and powerless DCBL. You can safely ignore anything from them. However, do not confuse or ignore comms from their sister company, DCB Legal.
As long as Highview and, if necessary, DCB Legal have your current and correct address for service, then you don’t need to send a DRN. If your address has changed since the original PCN was issued, then you absolutely must send a DRN.
You are now waiting for a Letter of Claim (LoC), which will probably be issued by DCB Legal. When that arrives, come back for further advice.