Unauthorised smart phone debit order

My smart phone account was handed over for collection to Groenewald Lubbe inc by FNB. I made necessary payment arrangement with the collectors and made three payments to them but to my surprise FNB legal's Maanda Mutele also debited the full O/S R2 509 from my FNB saving account to offset the O/S balance. But now Groenewald Lubbe inc are harassing to make payments as per arrangement made with them yet the full O/S balance was deducted by FNB directly from my Saving account. I have spoken to Maanda Mutele via phone, e-mails but now he doesn't respond to my emails and call because to best of his knowledge my account is paid up &amp