I had sent an email that I no longer require their service weeks before debit order date

I had sent an email that I no longer require their service weeks before debit order date. So I didn’t use any data for the month of September I told them not to debit via email. Instead they debited thrice ans found no money and I incurred charges on my cheque account. This morning they debited another R795, which is not autheorised, still haven’t received my credits from them too.