billing issue

I did an upgrade on the 1st November with a package of R319 and had already had an existing account that i was paying R330 for it . On the 19th December 2015 when i went to Mtn at The Glen mall wanted to make a payment they told me i was owing R1300 of which i didn't understand why it was that amount . when the lady who was assisting me Ntombi checked on the system she noted that i was overcharged/ over billed. She sent an email to the head office but until now i still haven't received feedback regarding the query. <br> <br> When i asked the call center agents that i was talking to all the time when i was calling to find out of the outcome as to how long is the turn around time for logging queries they told me its 7 working days but until today no one has come forth with any kind of assistance.<br> <br> Please assist me urgently .