Momentum Insurance - Bad service for a simple cancellation - How much worse for a claim?

I have phoned in 4 months ago to cancel my insurance. I have never made a claim and the price of the insurance is slightly more than what others would offer. I would expect great service but not cancelling for 4 months is shocking. I went to the bank last month August 2018 and the bank rep**** that Momentum Insurance are the only ones who can cancel the insurance.