Begin drafting your defence immediately. You have three options:
- dispute the entire claim,
- admit liability for the claim and propose terms of payment, or
- admit liability for part of the claim, propose terms of payment for that part, and defend the rest
Assuming 1 or 3 above, begin with admissions, denials and "no knowledges." Go through the paragraphs of the claim. Where you do not know whether an allegation is true, say as much, e.g. "The defendant has no knowledge of where the plaintiff resides." Then, admit what is true, e.g. that you live where the claim states that you live. Finally, deny what is not true, e.g. that you owe the costs of a repair.
Once you have done this for every allegation, you will want to make a defence. Be concise: state only what is relevant to your defence. Stick to facts. What happened where, and when. Who said what to whom, when. Assemble facts that will create a different picture than the one composed by the plaintiff. Constructing a good defence may be an art, but it's not a dark art.
While it is often tempting to do so, do not suggest malice unless you can construct a persuasive narrative supporting this suggestion and can provide evidence for it, e.g. a document. (A screenshot of a text message may or may not be accepted as documentary evidence.)
Finally, wherever possible, make a counterclaim. This is known in Small Claims as a Defendant's Claim. This claim can be made against the plaintiff(s) or against a third party.