Disgusting customer service

I recently bought a 2l milk only to find that it was sour when we got home. This was on the 6th December. Since then i have been trying to contact your complaints department. The calls go unanswered and the switchboard operator has sent my contact details to the lady responsible and asked her to phone me twice already with nothing happening. An email was sent on the 6th December as well and to date there has been no response. This is disgusting customer service. Please can this be dealt with