Permanent Netstar subscription

I didn't know Netstar membership is supposed to be permanent. I sold the vehicle a year ago, notified Netstar and even today they are still harrasing my account. On the 15th of June I sent an email to cancelations department (Ref ***3), that didn't work. For now I'm stuck with reversing debit orders, I feel that's the only way to deal with them. Can someone please attend to this matter.