Unhappy iSmart customer

I had 2 accounts with them. One is paid up and the other is still outstanding and which I am paying currently. My problem is they keep on double debiting monies from my account. When I call and ask them to rectify the mistake, they promise that the mistake won't be repeated. I happened for the past 3 months where I asked them to refund my money. I only received one refund and 2 are still outstanding. Please assist