refunds for the payment deposit of windows

We have entered on to the contract with builder by the name of Brian Zingambwe . His company is Agisang general engineering project ( reg. NHBRC 1- ********** 1). He also told us that he is having another company for aluminium windows . We accepted the quotation that was R40170 and we paid R30000 as a deposit. The companynname for windows is Fairvalue Alluminium CC.He only managed to put 03 windows amounted to R4620. One of the windows when we tried to open *****s were falling apart handle broken. We notified him, he promised to fix but nothing till date. We asked him to cancel the order for windows , he refused saying he already made windows. He keep on promising to bring and install windowsbut nothing. We asked him again on the 30 November, this time he came with the story that we owe him the money for construction, for additional work that he has done. The additional work that was never mentioned to us as client. All along we only knew that according to the plan the house is 280sqm. Now is telling us about extra 62sqm that was never communicated with us.