Dishonesty

I am renting an apt since 2013. At the end of the contract in 2014, I have got contract extension with 7% increase which amounts R4280 per month. The so called Porfolio manager agent sent me the extension paper works where it is clearly mentioned that the monthly rent is R4280. However I keep receiving R4400 statements. I then called them to sort it out. The agent(Clinton Moodley) told me that he will take it to his boss and call me back. He never did so. I called again and he asked me to send the contract and I did. When I called him back again he said I shouldn't worry because these R4400 are automatically generated by a computer. Yesterday when I got home from work I found a letter from a lawyer threating me because of a breach of contract. It's so irritating to deal these people. I am not sure the owners are aware of these dishonest behaviors. I don't have time for this. I will pay whatever they ask me but they have to remember : you can fool some people sometimes but you cannot fool all people all the time.