Handed over to legal without my Knowledge

I have a contract with MTN and have upgraded last year July/August 2014. My payment method is on debit order. Since January this year 2015 my son's phone was not working and I took it for repair. When it came back I then realise that the sim card is not working. Debit order of R735.31 went through on the 31st of March. I then went to the store on the 13th April to enquire why my phone was not working and why the debit order of R735.31. They told me that my account was handed over and they told me that they will contact them tomorrow and come back to me. I went there in the afternoon and the consultant told me that he could not reach legal department. He said he will write an email (14th April) and they will respond within 48 hours. I went there on the 17th and I was told that there's no respond ***. Legal department is not responding and I don't receive MTN invoices. I went again on the 28th April and still no response from legal department. MTN is not giving me the service that I am paying for and they don't send communication. It seems as if no one bothered to change my address after I have upgraded. They have my other contact number and I have never received a call or s