Feeling harrased

I sold a house in 2009. Every account regarding this house was cleared before It was transfer to the new owner. Since last year or a year before last I keep on getting phone calls from the company called MBDCS telling me that I'm owing Emfuleni Municipality. I send them the proof of payment and the transfer document but still the keep on calling me and sending me sms's and I feel harassed because I know someone is not doing her/his job. This Saturday around 13:07 a lady called me telling me that they are recording their calls. I told her if their are really recording their calls she is not suppose to call me because she will revisit the recorded call but she didn't take me serious eventually she was rude to me.