You use your MCOL account to enter a defence, do not counter-claim, and your defence should be along the lines stated here, that you are not liable because the driver has not been identified and Smart did not comply with the requirements of the legislation to transfer liability to you, the registered keeper.
Feel free to post your intended defence here first for comment.
DCB Legal won’t back down yet, you have to follow the process including mediation and submission of your N180 form, allocation of the case to your nominated court, but DCB Legal almost always discontinues before having to pay the court fee.
Search the forum for many, many similar cases.
8 June is now the deadline to submit a defence, so plenty of time.