********** and ******* debits on my account

I cancelled my warranty cover with M-sure in August 2020. I received a confirmation letter that stated that my cover will cease on 1 September 2020. This company has been debiting my account since September 2020 until now. How do I stop I stop this ********** and ******* act and also get my refund as I have a letter that stated that my cover has ceased after I cancelled it. Policy number ***