Put under duress

I have a cell c account with cell c however a while back I took out a contract with cellc for my ex girlfriend and I submitted change of banking details to the cell c branch when the deal was done it was going of my ex gf account. However my ex gf called cellc and changed her banking details. So I was contacted by this arrogant lady today who told me I have given them the wrong banking details which they have no proof of. I clearly stated when I called them when I renewed the contract that I will be making a cash payment to them and no longer debit orders. This lady put me under duress today.