Pioneer Foods shocking service!

At the end of May I contacted Pepsico/Pioneer Foods customer care centre and notified them of a 1kg Box of Pronutro that I opened which had a stale smell and was lumpy. They got all my info to fetch the box and would supply my with a voucher to purchase a replacement. Since then I received a Case Number and nothing else. I have contacted them several times where they promised that they will get back to me and supply me with a voucher. Still nothing! How can this large company give such terrible customer service? All I want is the product to be replaced!