Cancellation seems to be impossible!!!

After 10 years with Netstar, I sold my vehicle at the beginning of March 2024 and cancelled on 3/3/2024. I have multiple cancellation references, I've called, spoken to call centre, accounts and debt collectors. I paid until the end of April and still I am receiving invoices, threats of bad debt review and phone calls requesting I pay. The one guy in bad debt said "we'll just keep calling you". This morning I received another invoice dated 1/6/2024. Don't get stuck in the Netstar whirlpool!!