Product with ****roaches in / No voucher received

I bought a box of Tasty Wheat on 28 March 2016. When I opened it on 29 March 2016, there were small ****roaches in the pack, even though the expirey date on the box is only 17 November 2016. I phoned the customer care and was promised a voucher via sms within 5 days. It is almost 2 weeks later, and I still haven't received any voucher. I also sent an email to customer care, on which I have also not received any feedback.