NOT GETTING WHAT WAS PROMISED !!!

I decided to try a new ISP for data and searched the web. I contacted a Vox Telecom employee to get more info and he told me that I would download data at 3.9 Mb/s on a 4Mb ADSL line using VOX TELECOM 4MB FATPIPE, which sounded great and so I signed up with VOX TELECOM. After my account with VOX TELECOM was opened I had problems with slow download speed of under 2.5 Mb/s and also intermittent connectivity !!! I spent a lot of time on the phone over a few days to sort the problem out with VOX TELECOM support. After a few more days I switched off VOX TELECOM . I contacted VOX TELECOM and asked for a refund because they did NOT supply the SPEED PROMISED by their employee, which is breach of contract. Dawn at VOX TELECOM said I must pay an extra month as a notice period but I am not happy with VOX TELECOM and I want a refund !!!