Structural Engineering services Gauteng

My company has done hundreds of drawings for Mothoka Trading, AKA Tes Group. We have only received half of our payment for the work done and they keep avoiding us to pay the rest. We have done work for the Ford Factory in Silverton Pretoria on the upgrading of their manufacturing plant. The project was awarded to Durr in England and they contracted Mothoka trading out to do the manufacturing and installation. We did all the manufacturing drawings for them, 3D models, part drawings, assembly drawings etc. Our team worked 16 hour shifts for two months 24/7 and they are just not paying us. I dont know if I need to take legal action or what my next step needs to be.