Cannot get through to Cancellations for 3 days now

I have been calling MTN customer care call centre 3 times a day since Monday the 9th Feb to have my cellphone contract cancelled and to migrate to prepaid. With each call, I wait about 15-30 minutes to speak to a customer care agent, who then transfers my call to cancelattions and I stay on hold for about 45 minutes to an hour unattended. To date, I have not been able to get through to Cancellations. My airtime and data bundles get loaded on the 13th of every month, meaning, If i am not migrated by Friday the 13th Feb, MTN is going to load airtime and bundles that I cannot afford anymore and my bank account will be debited with R439 come 01st March. I do not want this contract no more, can someone assist and cancel it. I was told by customer care agents in Jan 2015 to call for migration in the week of the 13th Feb to ensure I do not get airtime loaded and my bank account not debited on the 1st of March. Now I am calling repeatedly but cannot get through to Cancellations. Cancellations office operating hours is 8am-to-5pm. I try in the morning, midday, afternoon, but to no vail. DEPRESSED!!!