I want my money back!

I requested to have my account cancelled for end of May. I paid my last R250 at the end of May and service was cut on the 31st of May. I was charged again this month for something I have not used!!! I want my money back please! I installed Fibre and I have not used my pocket router that has the rain sim card in! How can you charge me for something that has been cancelled and I have not used!