Unauthorised billing

LinkedIn offered me a free month trial for the premium subscription to experience the premium offerings. I was charged R479 for December and January (R950 in total) when I didn't authorize the app to do so. I went to the LinkedIn website to request a refund for Decemeber but no one ever got back to me. This is utter nonsense. For such an amount, you need to request the user's permission to charge them for the 'free trial'.