You first of all need to find out the status of your case.
Then, if you need to file a Witness Statement the courts are usually lenient on defendants if they’re only a day or so late. But, hopefully, you won’t need to, so get the status first.
If the fee has been paid and the claimant has submitted a Witness Statement then (a) you need to complain that you weren’t sent a copy (b) you need to get a copy and rebut anything you disagree with in it and (c) you do this by submitting your own Witness Statement.
Above all, you’ve got to ensure you don’t get a default judgement made against you because you didn’t follow the court’s instructions.