You should have been served with the claim form by the court. It may be that you moved.
However to set aside judgment it is not enough to say that you did not receive the court papers but you must also set out what your defence is to the original claim. If you do not have one then the claim will not be set aside.
If you have no defence you could pay the claim and write to the court explaining that you have never received the papers before and so you have satisfied the debt within a reasonable time of being made aware of it and requesting it should be removed from the record of County Court Judgments.
I there are any further points please reply and I will be happy to respond