Worst Service Experience with Cell C

My father cancelled one of his Cell c contracts that I was using with a immediate cancellation fee of R3200 on the 8th of June so that I can take the then prepaid number and apply it to my new contract

Now I'm going to be charged another R2400 on my first debit order on the 15th of July for the same cancellation fee which as stated above has already been paid and proof of payment has been sent through to Cell C

I went to the branch to sort this out and a case number was given to me for a payment allocation. This was on the 5th of July. I have been trying constantly since then to get feedback to resolve the issue. I have also made Cell C aware numerous times that if they don't resolve this issue before my debit order date of the 15th I will cancel the debit order through my bank and they will receive no payment from me until it is resolved

This is the worst service I have experienced in my life. I sorely regret taking out a contract with this company. It's extremely easy for Cell C to charge me again for something that has already been paid. Why then is it near impossible to resolve this matter which is their mistake in the first place?