Unauthorized deduction

Motor Finance Corporation added products to my Finance Contract without me signing for it or without giving them telephonic instruction to do so. They now keep on deducting these products. I did forward cancellation forms, but they said they did not receive it. The point is why must I forwards these forms anyway if I did not authorize anything. This pathetic and I am sure also not in line with the NCA. PLEASE SORT THIS OUT AND PAY BACK THE MONEY!