So, you arrived back on 23rd September but your defence deadline was not until the 30th September. Then, the claimant left it for nearly another month before requesting the CCJ in default on 24th October
You have a couple of choices. Pay £303 and try and persuade the court that you screwed up bit should be allowed to defend the original claim. Or, just pay the CCJ amount in full and be done with it as it will not be on your record as long as it is paid in full by the 20th November.
Unless you’re able to get help with the fees, in which case the first option is the way to go.