Struggling to get trough to call centre

I recently upgraded my contract. It was for a new Samsung galaxy tab 4 7 inch on a 1 gig day plus 1 gig night express . When I upgraded it was on the 18 th of April. I was given data according to pro rata . And had night express. As soon as it was the new billing month I only received my day data . No night express have been issued on my contract . Yet that is why I upgraded my contract. I've been trying to call 808 for the last 2 weeks and get cut off all the time. It's making me angry as what is going to happen to my 1 gig night express when my new billing month approach . I'm getting a annoyed at this no response from the call centre.