Struggling to Cancel Service

I selected both my Voice and ADSL to be cancelled via online cancellation but only my ADSL was cancelled in the end. I realized this when i received an invoice for the active Voice line.

Chatting to a consultant online they were not able to tell me why the Voice was not also cancelled with the ADSL as requested. I restarted the cancellation process and will now have to wait 30 days again for which i will be billed for. I am weirdly convinced that this is a money making tactic and as a customer you powerless if they fail to cancel, you just have to pay for a service you are not using.