You've only shown us the reminder. We would need to see the original Notice to Keeper (NtK) that was issued. It is far too late to appeal anything now.
However, as this is ECP, if you follow this advice, the Keeper will not be paying a penny to ECP. What is going to happen next is a stream of useless debt recovery letters which can be safely ignored. Debt collectors are powerless to do anything except to try and persuade the low-hanging fruit on the gullible tree to pay up out of ignorance and fear.
All debt recovery letters can be shredded and used as hamster bedding for anyone cares. Never enter into communication with a powerless debt collector.
Eventually, a Letter of Claim (LoC) is going to be received from DCB Legal. When that arrives, come back and we will advise on how to respond.
In the long run, a claim will be issued and we will again advise on how to defend it. Eventually, the claim will be discontinued and that will be the end of the matter but it is going to take anything from 9-12+ months.