frustrating

I had a terrible customer services which costed me 100% financial lost on a business that I did with them. I requested a quotation in writing which was going to help me quote my client and serve it. They gave me a quote to the amount of R5257. which I then marked up and charged my client 10%. Later when I return to them I requested them to validate the quote since its been long. They validated it telephonically and in writing. I then requested a proforma invoice to pay them. To my surprise the proforma came to be R7257 more than what was confirmed just few hours ago. I paid since I was late to deliver. Upon delivery I received the goods not as I have requested. They were less with about 41kg when I requested 50kg on two items and on the other item I requested 14kg they delivered 6kg. I went back and ask what the problem. They admitted they made a mistake and promised to correct it. To my surprise they corrected by sending me another proforma amounting to R3834. This now means I was going to pay double the amount they had quoted me initially. Remember I have quoted a client only 10% on those goods. This then means I lost 100% to Bidvest food because of their mistake. I spoke to the sales person she refused to reimburse me for her mistake and choose to apologies verbally and referred me to her manager. Who accepted the mistake and promised to come back to me. Later she comes back , acknowledge that they make a mistake with the first and second quotes they gave me, however she blamed me for paying the second wrong quote and suggested I accepted their fault therefore I need to pay the third quote before they can deliver. I find this to be very wrong that now they shifting their blame to me suddenly. As we speak my client is waiting for delivery I am scared to pay them and ask them to deliver because if they make a mistake and I pay they will say its my fault. I need to go get another service provider this time of the year where will that be? I am very frustrated.