Bad Service provider

I was called by On Air Tv who claimed that they are from multi choice and I need to change a decoder. I have called to cancel and ask for the contact that they say I am in but I am being sent from pillar to post. They have been taking an amount of R259.99 for a decoder that I don’t even use. Now that I have checked my credit report they have increased the amount without my consent. I want this subscription cancelled and they can come and take their decoder.