MTN not responding to query

Last year 2014 April/May I cancelled my one contract *** with MTN. Paperwork was filled in, I was assist by Ettiene that is still working at MTN River Square, Three Rivers. Beginning January 2015 I did an upgrade on my sons nr ***. End of January I paid my account. One week later my sons phone was blocked. I was told that my account is not paying in full. Only to realize that they never cancelled that contract and that I own them round about R1000.00. MTN Three Rivers was helpful and unblocked my sons phone after I explained what and when we cancelled the contract with them. Since then every second week my sons phone get suspended. Then I have to go there just for them to unblock it again. Then because they couldn't get this query solved, Celest at MTN T/Rivers gave me Isabel van Wyk's cell nr and email address. My first mail to Isabel was on 23 April 2015, explaining what happened. Every week since then I had to follow-up on how far they are with this query.Every time she is telling me she will follow-up on the query. 14th of May I send her a mail again, with reply on the 18th she will follow-up again. Account was blocked again and is still blocked.No one can help me