Overcharged since moving to MTN

Been billed incorrectly since joining MTN from Nashua Mobile. They have issued a credit on their system of R1300 that has never materialized into an actual credit to my account. In addition they have been overcharging my account for R250 description, H/W fees. Every store that I have been to has admitted the overcharge but cannot do anything except send emails to head office. Fact: MTN stores (the ones that I have been to) can only correspond with head offic via email. If the store wants to get hold of head office they need to use the same call centre line as the public. This is not a company that I will be doing business with in the future! I am willing to follow the legal route to cancel this contract should these issues persist as it has been over 6 months now. I would also encourage the general public not to take out any form of contract with MTN due to the fact that it is so difficult to communicate with them. Go figure a telecoms company that cannot communicate properly.