They don't stick to payment arrangement

I have never had any issues with teljoy. However I ordered a laptop and when I got it I was so unhappy with the laptop. I notified them within 4 days that I was not happy and wanted to either exchange it for a better laptop or return it as I was still within the time frame. Someone contacted me gave her the specs of the other laptop which was more expensive she told me that there would be an additional R700 for cancelation and I agreed to. Nothing came further of it. I sent countless emails and no response. I then asked that they please change my debit order from the 1st to the 25th because I changed jobs and get paid earlier now. Still no response. This resulted in twice the debit order not going off. I started to pay towards the arrears and got a SMS on the 8th Aug with my balance of R3800 which is outstanding I then was contacted by a lady and sent her a email stating that I would pay the current and an additional R1000 per month towards the arrears. She didn't even respond to my email just sent me a Sms stating that I needed to pay the R1000 as promised by the 25th. I had already paid the R1000 on the 25th and thought it was okay. This meant that I owed R2800 on my arrears. But then today the debit order goes off for the R3800..... they didn't even take my payment I made on the 25th off of my balance. Now I'm going to struggle to get the over payment back from them....stuck with a laptop I don't want and am paying for....like I said I have never had a issue but this is where I draw the line.