Forced Payment for a cancelled service!!!!!!!

The only reason I am even selecting a star is because I cannot write without rating. On the 01 Mar 2024, 11:31 I sent an email informing mix telematics that I can no longer afford to pay for this service and I want to cancel it, I received a reply email from them on the 04 March informing me that the service has been terminated with immediate effect.

They debited me on the 15th of March and I spoke to my bank and reversed the debit. Their debtors and mid collections departments have been sending numerous emails saying that I am in arrears and I should make payments.. I have paid for this service for over 9 years and now that my financial situation has changed, I get to be harrassed and threatened to pay for a terminated service, WHY WHY?!!!