Cancellation of debit order and refund

My name is Mpho Ramoejane. At the beginning of November 2017, I entered into an agreement with YelloData that they will provide me with Data. But by the end of the month, they still have not provided me with the data as agreed. I then terminated the contract with them but they have already debt my account. They continued to debt my account until 22 December 2017. I tried countless times to communicate with them that they must stop to debit my account which they did not. They asked me to send them my bank statements as proof which I did several times but they still did not solve the problem. I even took them to credit ombudsman and they promised to solve the problem but they did not and that was two months back. I would like them to stop the debit order and refund the money they have debited as soon as possible and no later than end of January 2018.