Can I be taken to small claims court?

Hi everyone, 

I am a caterer, I run a small mobile pizzeria.

5 days ago someone got in touch with me regarding a private party. I also been asked for an invoice, which was sent last Friday. Now I don't want to do the party any more due some other circumstances and this is the reply to my email.

The person is now claiming that I am contractually obliged to do the party, and saying that they will take me to the small claims court (claiming the additional costs in appointing a replacement and legal costs).

Note, the money has not been payed in yet.

Is there anything I can do about it, or do I need to find a way and just do the party?

I hope someone can help with an answer.

Many thanks,