Can you evidence that you were away between the date of issue of the Claim and the deadline for submitting the Acknowledgement of Service (AoS)? With an issue date of 2nd October, you had until Monday 21st October to submit the AoS which would then have given you until 4pm on Monday 4th November.
Simply telling us you "just got back from your holiday this week" doesn't give enough detail. The claim form will have been deemed served by Monday 7th October. What date were you away from?
What date did you actually get back? Was it after 25th October? If you could have done so, even if past the deadline for AoS, have submitted it up to the 25th October.
So, dates please.
If you want to apply for a set aside, you will have to do so under CPR 13.3. The claimant has not erred in applying for the CCJ in default. A set aside application under CPR 13.3 is a discretionary set aside. If you can prove you were not aware of the claim because you were away, your application should be under CPR 13.3(a) and 13.3(b)(ii).
If you were to pay the judgment amount in full before 22nd November, it would be expunged and you would not have a CCJ on your credit record for the next 6 years.
So, two choices really. Apply for a set aside, especially if you can evidence you were unable to Acknowledge service before the default CCJ or pay it and that will be the end of it.