ADT is claiming that I owe R11 833.60 for security

ADT representative presented a product on promotion during Dec. 2013. I was interested in the product until I realized that there were hidden amounts to be paid by me later that he did not disclose. I immediately asked of those amounts and he said he will speak to the manager to change the contract then call me the following day so that we sign on a new contract without those amounts. I called him before he called me and I told him that I was no more buying the security system from him due to misrepresentation of information he initially gave me. We both agreed and that was the end of the business, we never went to the stage where they installed the system in my house as the deal was cancelled. 3 months later, I received a statement from ADT, I called and explained and the consultant I was speaking to said it will be cancelled from their side. I thought that was done and all was in order, only last month, I received a message from DebtSource collection on behalf of ADT that I should make a payment in 15 days. I sent an email, they called me and I explained, they said they will investigate and come back to me. Today I opened my emails and find a statement with an amount of R11 833.6