Unpaid contractor

I own a construction company and last year I did work for King Price for their client whose home had been damaged during the kzn floods. The job was completed, proof in the form of pictures was sent along with the invoice to King Price for payment but Delini who is the lady that was assigned this case has treated us so badly as if they would be doing us a favour in making the payment. All the repairs were paid for by my company, there was no payment received from King Price for us to do the job. King Price sent one of their managers to the clients home to confirm that we had indeed done the job and their manager was happy with the work done. It has been 4 months and we still have not received payment. We have lost other work as a result of wasting our money doing this job for King Price. My attorney has sent a letter of demand but I intend to sue for the financial loss that we have suffered as a result of doing this job. To any contractor that might consider doing work with King Price, please save yourself from the hassles and do not accept any work from them