Poor service at Wesbank

I'm financed by Wesbank on the car that I bought. There were some value added products included when I bought the car which I later cancelled but to my surprise those products are still included in my monthly installment. I have a year now sending them proof of cancellation for those products but they keep on saying that they cannot make amendments because the confirmation letter of cancellation is not enough although a refund made to them. Please help as I've been paying for things that I'm not benefiting from 😭😭😭