Shocked client

I received a call from this company selling a decoder that was on promotion. I completed a telephonic contract and the device was delivered at my mom's place in Pretoria. 3 months later the was not installed. I decided not to pay till the installation was done but that never happened. I then req to cancel the account and let them fetch the device. They kept on sending people to my house to collect and I told then the device is where it was delivered in Pretoria. The next moment I received calls informing me that I have been handed over and black listed. I was shocked to be called by 2 different people with different amounts of money that I owe on Air.