Landline not disconnected after 5 months

At the end of August 2017, i app**** for my landline to be cancelled. filled in the necessary forms. no one contacted me. i noticed that i was still charged rental. Worse, there is new occupants in the building - what if they plug in a phone & use the line. I logged a dispute. An agent called me & advised that they will credit the rental & refer this to the order section. 2 months later, no response. I again call the callcentre to query why the disconnection has not gone through. "We are on a new software program" they say.