7 Day Notice Prosecution, fake?

Hi everyone,

I have recently launched a small business as a sole trader, and was enquiring on different websites for a quote to have magnetic stickers for my car. Several companies sent me an artwork of what they could do, with a quote. I agreed with one of them, made the payment online, and was very happy of the result.

However, one of these company came back to me by phone and email asking me £18 (!!!) for the "artwork" they did-and that honestly took them 1 minute at the maximum!

I simply told them that I did not want to go ahead with them, and that I did not agree anything, nor signed up anything. I also sent them afterwards an email saying that  I was not entiteled to paying them anything because I did not use their service, nor purchased anything from them.

Today, I received a "7 day notice of prosecution" from them, (not a law firm nor a lawyer), asking me £18 again, within 7 days, otherwise blablabla... adds £40...8% interest...

What should I do with this, considering the circunstances please!?

Many thanks in advance for your time.

Regards.

AB