Poor service! No help!

I phoned MTN to find the amount needed to be paid for a wifi contract to be cancelled. I was told the amount. I paid the cancellation sum on the 6th of July, but I was told it was too late to do the cancellation when I phoned them after I paid on the 6th, so I could call the next day to do the procedure. I asked for the cancellation on the next day (7th July). I was told on the 7th that the cancelation will be done , but the system is down and they will be processed until they are online. On the 10th of July, I phoned them to find out if the cancellation was processed and they said the number no longer exists, meaning it was cancelled. A few months after I discovered that for my phone contract, which is different from the wifi contract, they are not taking money from my account, so I phoned them to find out why that is so. The wifi contract was not cancelled, I was told.Instead of the cancellation , the money that was originally paid in for the cancellation of my wifi contract was used for my monthly contract payment. They Processed the cancellation only after this enquiry.I was then told to pay an unpaid balance for those months when they didn't take money out of my bank account. I phoned again to find out the bill because i wanted to pay it in once they have the correct amount billed. I was told that I would only know in the next month. Then it was higher compared to what I was initially told . After that, I've been continuously calling to figure out why it was high and they kept saying they're going to escalate the matter, but it seems like they haven't. They also said that they were going to investigate it, but they did not. Then they put me through the department of retention and I was told I had to pay a certain amount and I was going to be compensated with the remainder. On December 4th, I paid the amount and I phoned back to tell them that I also paid the amount to inquire about the compensated amount I was told about, but they kept saying they would investigate the matter and escalate it. Still no reaction or help, now it's gone to a point where my contract is suspended, and have assured me that after I make payment, the additional amount will be credited to me.i have proof of payment, reference numbers.