I paid my contract so stop harassing me

Good day. My name is kagiso. I took a 2 year contract with mtn. I finished paying them in October last year I still have their statements. To my Suprise after that they were sending me messages to pay the sum of R180 so that my contract can be fully closed. I refused cause that was not part of our agreement. To my Suprise again they claiming that I have been handed over to their lawyers as m owing them the sum of R1834. I am tired of them and I want them to remove me off their system. I have all the statements and in all their statements they never mention hidden costs . I am tired being harrased by mtn with their nasty sms's. They never call me, they only sending me unending and annoying sms.