what is the point of customer service?

I once sent customer service complaining about the quality of tinroof ice-cream. I first inboxed Woolworths on facebook and was asked to send an email to customer service which I did. on 23October I received a response apologizing to me and promising a R70 voucher which I am yet to receive. again on 17November I sent a email again complaining about the same product and a voucher that never arrived. What is the point of customer service if we are promised things with no response