I am sure there is a topic with similar issues, but my in my case it is small sum involved that makes it more moral issue than financial.

I thoughts of starting to have some design jobs on the side my full-time employment. Registered with my local office and was happy with my first own client, who asked me to do a leaflet. I thought will take me about an 2 hours to do, and we agreed on £25. Send him designs, he liked it, done some adjustments. Then he said he will have to come back in 3 weeks, because his director is away. He did not, after me contacting him asking for payment, he stated that they did not use my design, therefore there will be no payment. I know it is little money, but I hope there is a way to show those people, that they have to keep to agreement. Would you know what could I do?