Bad customer service

The worst service one could ever have. I had contract with them for the mobile data for R250 and their invoice came with R2600, just when I thought maybe it's the pro-rata then boom another invoice with R1800 for a R250 contract worse they claiming they have given me the minutes and I have never used any voice calls.Now I called to cancel my contract they gave me a cancellation fee i payed it at their branch now I'm told I should have called immediately after I payed a cancellation fee. It's if very sad that the agent hunged up on me when I requested to speak to the supervisor. Bad customer service ever.