Budget keeps deducting 18 months after cancellation

Our vehicle was covered by Budget Insurance for a while. The vehicle was sold almost 2 years ago and the comprehensive insurance policy cancelled. Unknown to us the add-on for Scratch or Dent was never cancelled and because its R99/month we never got notifications from the bank. Now we have to proof to them that the vehicle was sold before they are willing to refund the ******** deductions they have taken even though they have record of the comprehensive insurance cancellation. Surely an add-on should be cancelled when the comprehensive policy is?