Rotten Custard and Bad service

i am very ****ed right now i bought a G-free dairy custard and the expiring date on the package was January 2016 and i bought it in November and when i opened it i found that it is already rotten and has maulds and then i immediately called the customer care and i was told tht it can happen if it is not properly packaged and then i was promised that they will send me a voucher and up till this day im still waiting for a voucher and i called 3 days back i spoke to Nicole who took my details and said she will call in the next hour but never did its been 3 days now waiting for the call. What im receiving from this people is a bad service because now its been 2months waiting for my voucher, and i get very ****ed because i used my money to buy things that are rotten yet they dont even attend to their customers