Only made an enquiry - now getting harassed for being payment!

Please don’t ever make an enquiry with Cartrack! I made an enquiry online and when they didn’t get back to me, I went with another company. Now 6 months since my enquiry, they are harassing me for payment! When I call them, they tell me they have me as an active client, even though I never returned any paperwork! Asked them to “cancel” and they claimed to have processed it but I’m still getting harassed for payment.