Insurance ********** behaviour not processing a cancellation and *****ing my money

I've cancelled a cellphone contract including the insurance on the device more than 4 months ago. I requested a cancellation and the consultant advised the last payment would be deducted month end I agreed. Then they billed me for October November and December. The last deduction was suppose to be September as the cancellation was done 30prior to September. Is this how you say thank you....