Overbilled since January!

On 29 January, I went to the Fourways branch to downgrade my ADSL package from 20 gig to a 10 gig package. After standing in a queue for a very long time, I completed all the necessary forms and was told the switch would take place on 2 February. Since then, I have been billed for both the 10 gig and 20 gig packages. On 7 May, I called the call centre. After being on hold for a very long time, I spoke to a consultant who said that I would be contacted within 3-5 working days and if I did not hear from anyone I was to call back after 5 working days. The reference number is ***1. I called back on 14 May and was told I would that I was wrong and would receive a call within 9 working days from date of lodging. It is now over a month and no one has contacted me. I am also still being overbilled. On 7 June (a Sunday) I received an sms to contact their cancellations department. I was on hold for 20 minutes with no one taking my call. I don't want to cancel my service (but perhaps I should), I just want the overbilling corrected and credited to my account.