Bad treatment by Letcor Property Management

I'm so furious at this agency, I moved out of their flat in July 2017 & yesterday a woman by the name of Precious told me that they have been charging me rent until September 2019 & when I ask her under which grounds she could not give me an answer she told me she will investigate and call me but she has not called me until now, when I call back she does not want to come to the phone and speak to me I'm answered by a rude guy who ended up dropping the phone on my ear. They have even blacklisted my name for that. I'm calling them to fix the issue but they are not willing to do that