POOR SERVICE - UNPROFESSIONAL - DELAYED- *****

I have taken a contract in 2012 which was a 2 year contract for a laptop. I never used the Sim card for the modem as i used to but my own data- hence still paid them the subscription fee each month which was supposed to be R250 pm but every month was increasing.There poor service from the start - no ones get back to me, i send numerous emails, i called their head office they refer you back to the store - then when i call to speak to the previous people I dealt with they left the company or not avail. We are customers not toys and we all work hard for our money I do not wish for anyone to experience the terrible service and attitude I received . now 2 years later after me actually paying this account in full to close the contract - i get a letter of final demand for R900!!!!!! FOR WHAT I DON'T KNOW. I am a debt counselor and I will be approaching the NCR with this matter.