Continuous excessive billing

I had three contracts with Cell C; two mobile phones and one tablet. The contract for the tablet expired last year and only after a couple of months was I informed that there were still outstanding fees. After paying them, the amount was still deducted from my account and I had to provide proof of payment twice (each time being assured that a \note would be made on my account\"). Skip to the beginning of this year: amounts higher than the normal monthly amount suddenly appear on my debit order. I have been to Cell C Tygervalley to rectify the problem, yet faulty amounts were still being deducted. Today I was phoned by a Cell C representative who wanted to know why the tablet is not being paid, although this issue was resolved months ago (or so I was led to believe). During the same call I was informed that no note has ever been made on my account. Do they even make these notes? I have tried to sort out these problems by going to the mentioned branch at my own expense, yet I fail to see any real effort being done. I will not be renewing my contracts with Cell C (although I doubt the debit orders will stop), but I believe other potential customers should know what they could be in for"