Mobilechoice account wrongfully handed over

I took out a cellphone contract with Mobilechoice last year around June 2014.On Monday 26.01.2015 I received a call from DMC to make an arrangement for payment on the mobilechoice account of which I was very surprise and the consultant told me that the account was handed over to them the same time I took out the contract.I have to account with DMC of which I am currently paying and she requested a R50 increment on the other 2 accounts of which I agreed.Yesterday the debit went off double with the normal installments and the increment installments.I called them to reverse the to normal installment since the increment installment went off . supply I even requested a letter of prove to show @ the bank in order to reverse of which they promise to supply me with and u[p until now they have been ******** and I have never received the letter