DBI Consulting in Centurion , a big company refusing to pay me for the work done

"DBI Consulting in Centurion " I did IT work for them , spent a month going to their office doing all the work . Now they just don't want to pay me my money , let alone refund of the cash I used to buy material etc .

How do I get about this situation ? They owe me about R15000

I have all the emails , recorded calls and SMSs