Fine Golding not settling their debt

Fine Goldings approached our SME company to manufacture an Outside Inverter box to their specific requirements. Not an item that we normally manufacture. They pushed us to get it done within a day, which we did. 3 months later we have still not been paid. We have called them directly, visited their office numerous times, emailed them, but Nicholas Glaeser (the director) does not take our calls and don't reply to emails or phone calls or messages. Numerous times I have been to their offices, but the 2 x gentleman in the office - Roland and Luke - just empty promises. The invoice is now outstanding since the 4th May. Apart from not paying their invoice, they are truly very bad at client service and responding.