Cell C Insurance not terminating insurance

I requested termination of Cell C Insurance on my phone 3 months ago. I did this telephonically. To this day they still have not cancelled it and continue to raise the debit order and pull the amount out of my account every month. It is absolutely impossible to get hold of them on their helpline - it just goes into a permanent loop. I have emailed them and the underwriters, Finrite, and they all just ignore me. I am getting nowhere with them. This is unacceptably poor service!