No response on complaint about charges

I took out a contract with Vodacom. I migrated after the first month and they added a charge for a handset. I explained to them that the charge is being added unfairly and they said that it should have been added with my original contract. At that stage I could not find the documents showing that a handset is included. I later found the document and logged a query to say that they need to refund me for the handset charges and remove it from my account. It is now a month later and after various calls I still have not had a response from them and the query is still not sorted out. My account is still being billed with this charge. I have 3 contracts with them and am so sick and tired of having to fight for them to pay my money back. I pay my account on time and have been a client with them for 4 years. I am disgusted with the service that I am receiving!