Cancelled policy, but money still going off

I cancelled one of my policy’s at standard bank in December , but they kept on taking my money every month. I sent emails explaining, but nothing. Until I put it op hallopeter, they helped me very fast, but they then told I have to cancel 31 days in advance that is why they are still taking my money so what they are actually saying is if you want to cancel something at standard bank you have to do it on hallopeter, because no one at standard bank read’s a email. I have sent all the documentation and proof of my cancellation to the people that kind off help me last time.