Telkom failed to cancel my contract & still debit

I emailed the cancellation form on 4/1/2016, the 24 month contract period I signed up for was over and I wanted to cancel and move to prepaid. However, I received an invoice due 29 Feb for double the amount I used to pay on my contract as they are now charging me for internet access which came free with my contract as I got it on special. I contacted them again on 4 Feb to enquire about this. The call centre said they have logged a query with the billing dept. They were supposed to contact me 72 hrs later, but nothing till today. I've heard nothing from the cancellations dept also. And to make matters worse, I have an unresolved internet connection complaint since about Feb 2015 when my internet connection suddenly started giving issues after being with Telkom for a year. I've asked for a booster numerous times but nothing. I have also asked them to reimburse all the data that expired as a result of me not being able to use it due to connection problems. None of my problems have been resolved, yet they want to keep charging me for a service I cannot use! Telkom, please cancel my contract, reverse the invoice due 29th Feb and refund all data that expired due to connection problems.