Very unhappy and disappointed supplier.

I recieved an order to deliver some groceries at the Cape Town Navy Base in October 2021.i delivered the goods on the 14th of October 2021. I was supposed to be paid within 30 days of delivery. I have been waiting for my payment since. When I first enquired in November seeing that a month has passed and nothing is coming forth,the explanation I received was that there was a mistake made on their system where my invoice did not match what's on their system. My invoice was half of what's on the system, however, they will fix it and pay me accordingly because my invoice was correct,the fault was on their side. My mother in law took up a loan of R205 000 for me to be able to deliver on this order, with the understanding that I will recieve payment withing 30 days and the loan will be settled. Due to the this delay, my mother in law had to pay the R6000 installment required to furnish the loan.It's been 3 months of painful survival caused by this delay in payment. I have made countless follow ups between November and December 2021, I was promised that the matter is being investigated and they will revert back to me. This has been going on for the last 3 months. I don't have a job, and this is how I survive, by delivering for government depts on small orders. I now have to repay my mother in law the R18 000 that she has already paid back to the loan, that's all the money that was supposed to be my profit, now it's all gone. I had to always be the one calling the NBS to get feedback and, no one has ever called me to offer me any solution. It is now January, I am frustrated and cannot believe I still have not received any payment. I have called the switchboard and try and get hold of the finance department and I'm told their phones are not working and there's no way I can get hold of anyone to help me. This is very frustrating, I tried being patient but my patience has run dry. I need help please.