Continual debiting for cancelled contract - rogue debit order!

In July 2019 I called and cancelled a contract for a tracking unit that was not being used and was in active for over 6 months due to the vehicle having been sold. Netstar continued to bill and not inform. In July it was confirmed by the call centre consultant that this would seize only after one month. Currently they have billed 3 additional months for a cancelled contract. This is one of the reasons I will not continue to support this company.