Account closed by customer but customer is still being billed

On 1 June, I received an sms from my bank regarding 2 amounts that have been paid to Yello Data. I did agree to have R59 deducted . But according to the sms an amount of R243.84 and R302.84 were paid. When I phoned yellodata, I was told that they were experiencing issues in the accounts department where some customers were billed incorrectly. Some of the money was refunded to me. I was unhappy that not all the money was refunded so I cancelled my yellodata contract on 9 June and I received a sms confirmation that it was cancelled. On 30 June, a payment of R59 still went thru for this cancelled contract. On 1 July, I received an sms saying that a payment of R59 has gone thru again although the contract was cancelled. This contact was again cancelled on 10 July. On 1 August I received an sms saying that R454 was deducted off my account. I emailed yellodata on 1 August regarding this and no one rep**** to me mail. their systems were also offline during this week and was told that I could not be assisted and needed to call back. On 7 August I managed to have my contact cancelled for the 3rd time. I was also told that yellodata is again experiencing issues on their accounts side where customers are being incorrectly billed. I was also told that my query will be forwarded to the accounts department. Its been 2 weeks and no one has contacted me on these issues. To me it seems that yellodata is running a **** with its customers. They deduct money off their accounts, collect the interest and then refund whatever money they think is satisfactory to them. This surely something that needs to be investigated. What happens to the interest that yellodata has collected for the money incorrectly deducted? If a customer agreed to have R59 deducted for a contract, why is there more money deducted? If a contact is cancelled, why is yellodata still deducting money for the cancelled contact? Why does a contact need to be cancelled 3 times? Are there procedures not in place at yellodata to ensure that if a contract is cancelled, all systems reflect this? What are the superiors/ managers doing about this? To the people working at yellodata, R454 may seem like small change but that's 45 loaves of bread.