UNAUTHORIZED DEBIT ORDER/THEFT

I am not sure how many times do I have to post a review about the ****** called iSmart. I have been fighting the same battle with them for years, but despite all the excuses they give, they still continue debiting my account for a contract that was paid up years ago. In March 2018 I asked them for a settlement letter and it was sent to me, so I paid the whole amount that I was outstanding. I have an e-mail that i received confirming settlement. They keep on debiting my bank account as and when they please. I keep on stopping and disputing the debit orders, they'll keep quiet for a month or two, then they"ll come back again debiting a different amount. I stopped calling them and asking the "whys" because their customer care consultants will tell you different reasons and different stories or send you from pillar to post. No one seems to know jack when it comes to why they keep debiting my account. The bottom line here is that I do not owe the company as i mentioned that I settled whatever I was owing in 2018 March already. Can someone with enough braincells in the company sort this out once and for all ?