Billed for inactive account

My son's cell phone was ****** around the end of his contract with Nashua Mobile in Sept 2014.<br> We blocked the SIM immediately and made NO SIM SWOP.<br> We bought a phone somewhere else, thus accepting that after 24 months the contract would end,<br> since there is NO ACTIVE SIM on the contract, but noooooo.....<br> They (Nashua mobile and now Altech) has kept on billing me for a service I don't have and can not use (blocked).<br> Their excuse is that I should have stopped the service after 24 months!!!<br> They contacted me about this, I just received bills, never looked at the phone no is was for until now,<br> to discover I have to cough up R1207 now to be able to stop the service or be handed to the credit bureau.<br> THIS IS NOT RIGHT - I can not be charged for a service the system MUST recognize as non existing!!!!!<br> An active SIM maybe yes, they can rely on the small print, but not this!!!<br> I can for the life of me, not get anyone from Nashua or Altech to assist me on this (no managerial assistance).<br> Any advice?