does that LoC have the same reference number as the previous LoC? Do you have more than one outstanding PCN with ECP?
The original LoC has the same reference as the actual claim you have already been advised to defend.
Make sure that this new LoC is not for a different PCN. If it is for the same PCN you are already defending, then this is an abuse of process and DCB Legal should be reported to the SRA.