Calls not diverted to voicemail

I have been trying to follow up for four days on a query about calls not being diverted to my voicemail but instead my line just goes dead. Your call centre staff put me on hold, saying they need to check the system. After 10-15 minutes of being on hold and listen to your annoying 20 second repeated marketing of opting into out of bundle rates, I hang up as no consultant comes back to me. When I logged this query I was told it would take 24 hours. Please can someone assist.