Harrasment from Cartrack

I sold my Hilux last year May 2024 , I informed Cartrack and was informed that i need to pay one month notice ,which i did as same was deducted on debit order. However since then every month they try and deduct the debit order. I am receiving 6 - 8 calls a day , I have informed them multiple times that I have cancelled the service on telecom , email and whatsapp. they now started to change the debit order amount in order to receive same as I stop the debit order by the bank.