MTN debiting my bank account when I have not had any transaction with them

MTN keeps deducting money from my account but the mandate they sent to me was rejected. I just received the mandate which I had no idea what it was for, rejected it, on the 25th a had a deduction on my account. This is very annoying because I have not communicated with MTN at all, rejected their mandate but still get a debit order and a debt listed in my name.

Remove this nonsense in my name or I will go the legal route.