Don't pay

We are a construction company that helps businesses revamp or whitebox shops they are renting. We where contracted by Cross trainer to do one of there shops in Rustenburg. After we tender and negotiate a price. They paid a deposit and done the work in the time frame given. Now that the workbis done they don't pay the balance. After multiple calls and emails the just ignore you. I mean a company that is nation wide cannot pay R40k for work that is done and just stay quite. It is shameful that big corporations do this to the smaller companies.