ACCOUNT MESS UP AND SUB-STANDARD DEVICE

I took out a contract with iSmart mobile for an Axxa mobile phone and I pay R285.00 per month. When I took out the contract I was told that this is one of the latest devices and it is a good phone I specifically asked as it was a not a known name device. In the March of this year I notified them that my salary date has changed from the 20th to the 25th of the month. I advised them via e-mail that my account is in arrears with R570.00 which I have requested they debit from my account. In March they did not debit my account resulting in my account being in arrears for 3 months now. I sent e-mails and have been in contact with them to make arrangements to get this arrears amount settled. In April and May my account was debited on the 25th as per the new salary date. I contacted them telephonically again to arrange to settle the arrears and was told that my contract period has been extended with another to 17 months to allow for the arrears to be paid off. I was quite okay with it and agreed to it. In June I sent them an e-mail regarding the device that is not working as I cannot hear people so I cannot or receive calls and the phone freezes all the time especially when I want to listen to voice notes and the battery live is also not good. At first I was advised to use my phone on battery saver but I told the lady that this is impossible and after that I was assured that the phone will be collected for repairs and was given 15 working days for this to happen. Toward the end of June I received an sms from their lawyers advising me that the account was handed over to them for collection and I needed to make an immediate payment of about +_R6500.00. Was I surprised after all my communication and confirmation that it was sorted. I e-mail them again to find out why and was told that they tried to debit my account on the 20th June and it was unsuccessful. I then found out that they tried to debit my old bank account which I haven't used for the last year hence their unsuccessful attempt. I again requested them to debit my account with R570.00 for 3 months to get the arrears settled and low and behold they did not. I am still getting calls from the lawyers to recover the arrears. I just feel this is completely incompetence from the company as to the way my account was bungled up and I am still with a device that is below standard and which I am expected to pay so much. They should be hones with their customers when selling their products