billing gor a service i did not subscribe to

I have been billed by Vodacom ( who has been billed by Waspa smartcall services) for subscribing to a **** site which I deny ever doing. Their response is that I mistakenly clicked\yes"on some sms which automatically started billing me on a daily basis. Neither Vodacom nor Waspa have been able to furnish with with substantial proof of what I actually did. I have requested a refund but they decline saying I did this. What course of action do I have from here on? """