CELL Cs bad customer service

In 2010 i took out a contract phone for my baby sister who was off to varsity,Cell C contacted me and they told me about what amount i would pay and the phone i was getting,the duration which was 12-24 months not sure ,it was not an issue i took it because it was a need at the time,I paid and in 2013 i decided to go study full time(no income what so ever) then sometime in 2014 i received a call from cell c informing me that i owe them for a contract,I was shocked and the lady was very rude to me ,refused to listen and just talked at me and hung up.on Friday i received a call From DIRECT ONLINE not sure of the name ,it was another lady who called and she also refused to listen and just talked at me.When a contract ends isn't it the company's responsibility to call the client and ask about renewal etc,i was not told i had to cancel after the contract period.I told the lady on Friday that i will not pay extra if i paid till end date what more do they want from me ,This was horrible service and they must team the staff customer service ,not impressed