Who do they think they are!!!!!!

I would like to formally lay a complaint against Miway insurance, they have on a number of occasion ignore my cancellation of policy I took with them. I have spoken to them since May, when I sold my old car and bought my current Renault duster. It saddens me that we are now nearing the end of the year and they still continue to deduct monthly instalments. I have resorted to requesting the bank to reverse their debits, I am forced to do this every month. This is having a negative effect on my credit score, not to mention the emotions and time I have to invest in this.