Terrible Customer Service

In July I changed from a 25mb line to a 35mb line. The salesman however did not cancel the 25mb line on his side. When I received my invoice I was charged for both lines. When I queried it with accounts I was told that they didn’t get the cancellation from the salesman so I have to pay for both lines. I have proof of messages from the salesman to say he has cancelled (in July) and have forwarded them to Vox and no one has come back to me. My account has now been suspended because I refuse to pay for both lines. None is able to assist me. Feeling absolutely helpless!