Contract Terminated after Payment Arrangement was made

On 10 November I was informed that one of my cellphone accounts was in arrears. This was a secondary line we only used at home for emergencies and when i was alerted that the account was in arrears I realised that the sim card was actually missing & I immediately asked the lady at Cell C to block the SIM. The sim was connected to my main account and this caused my main account to be in arrears as well & I spoke to a lady called Bella in collections to make a payment arrangement over three months. Instead of the agreed amount to be debited from my account, Cell C debited my account at the end of November with three separate debit orders, totaling to R11 000+. I then disputed the debit orders and we came to a new agreement that the outstanding amount would be paid via EFT. My intention was to pay the first installment when i receive my salary in December.

Cell C then sent an SMS demanding me to make a payment arrangement or my line would be cut permanently. The payment arrangement was made, but Cell C still proceeded to cut my line - so i now can't make or receive calls. When I emailed a lady in collections i was told that i did not honor my promise to pay and my details were handed over to external collections.

Cell C also did not honor their promise to debit my account as arranged, so I now i have a contract that is no use to me. Seeing as my line as been cut permanently, can cell c also go ahead and cancel all contracts as this is how they handle a customer of over 16 years.