Missing post is not enough sadly. The rules say you can apply to set aside if:
(1) In any other case, the court may set aside(GL) or vary a judgment entered under Part 12 if –
(a) the defendant has a real prospect of successfully defending the claim; or
(b) it appears to the court that there is some other good reason why –
(i) the judgment should be set aside or varied; or
(ii) the defendant should be allowed to defend the claim.
(2) In considering whether to set aside(GL) or vary a judgment entered under Part 12, the matters to which the court must have regard include whether the person seeking to set aside the judgment made an application to do so promptly.
So you need to have a defence to the claim, not getting papers is not enough.
You could pay it and then apply to set aside, that way you would be protected.
The court fee to make an application is £255 and you dont get that back sadly.
Can I clarify anything for you about this today, please?
If you need anything further I am available for a follow up at no extra cost.