No notification of premium increase

In August 2015, after receiving numerous sms's to do a cell phone upgrade, I went into Chatz cellular in Adderley. I decided to stay on my current contract of a reduced premium on a handset-free contract. I continued to pay the same monthly premium and then the calls from 082 275 97 started rolling in every month after I had paid my account. Until yesterday I got another call from the same number saying I had over R600 outstanding on my account which resulted in my account being suspended. I then went back to the same retailer in Adderley and was informed that my account was now on a month to month basis since August 2015 and my premium had increased. I was never, not once, notified of this. As a result of these late payment, the difference of what I would normally pay, was resulting in a bad credit score. Which I have been keeping up to date and in check as I am desperately trying to get a car. I am now, 7 months later, aware of the exact amount I need to pay. Vodacom must contact Transunion and have my bad credit removed from their database.