bad service

I sent an email to altech nestar last year august notifying them that I will be changing bank with my new banking details, but they didn't update on their system I ended up getting an sms from nudebt collectors telling me that the account has been handed over, I then try to call them and the guy named Thabiso lobai promised to change my banking details, I sent an email with proof that I did notify them but they didn't and I got another sms then I decided to write the matter on hello peter a lady named Nomsa Cindi called and promised that she was changing the banking details as we speak. There were no deduction on my account in Oct, Nov and Dec and I have been calling non stop and they promise me to change my details but they haven't until now and the arrears are increasing monthly and I have to pay them whereas they didn't do their job of updating my details on their system, the service I got from them is very bad I don't wish it for anyone and I would recommend altech to anyone. Now when I call they promise me to call back but they don't call back I am tired of this issue