Auto & General debit bank account after cancellation for 3 months!

I have cancelled this insurance in June but they continued debiting my account in July, August and now again in September despite numerous communications which they always lie and say they have refunded me on the 06 September, but they still continue debiting again in September! They now don’t respond to my emails! They have even sent a cancellation letter but they still do as they wish in my bank account and that is the reason why I cancelled the policy cause they’d debit on days that we didn’t agree on! Please assist, I need my 3 months premiums.