Rainbow Cake voucher promise

I bought a rainbow cake for my sons Birthday. Now we have bought this cake many times before but this time the icing was inedible. Not sweet at all and stated like pure margerine. I complained on the 1st of May and got feedback on the 2nd of May with a promise of a R350 voucher. Since then I have been sent from on Customer Care person to the next with no voucher in site! I have had to follow up 5 times now with no response from Woolworths. I expect better from Woolworths in quality and customer care. They don't care at all and I find this absolutely ridiculous. Latest reference number in the ridiculous back and forth ***