Billing complaint

I took a loan which was payable over 4 months. My first instalment being January. In January I called in and advised them to change my debit date from 15 to 20 going forward and I was assured that it will be done. The change was only done for January and I had to call in every month thereafter. In March I called in on the 10th March and requested that my date be changed to the 20th and also that they should debit the payment for April as well this was not done. A debit order went through on the 15th and I reversed it. On the 20th no debit order went through and it went through on the 2nd April. Two amounts we were debited R706.09 and R 1419.91, why was I debited twice as according to my knowledge either the R706.09 was supposed to go off which was the normal instalment or R1412.18 which would have been double payment and the account be paid up and closed. Now I am receiving SMS saying that I have missed a payment. I have sent numerous e-mails. I assured by Khanyisile Thwala on the 27th March 2015 that my debit date has been changed to the 20th of April and going forward the date has been changed to the 20th. Can someone sort this mess out and give me a resolution to this.