Dlink Router faulty

Mrs Nellie van der Spuy (77 years old) bought DLink Router from Telkom Vincent Park during first week of May 2017. DLink router only worked for a week then became faulty. She has requested over 13 times for them to assist her to fix or replace the Router. In May when the fault first occured, she took the router back. They sent it to the Service Department but advised her that nothing was wrong with it. She must check her internet ADSL lines. There were no problems. Everytime she phones the Telkom Fault line, they check and report to her that the router is faulty, she takes the Router in to Telkom Vincent, but they tell her that there is nothing wrong with the router. She does not know who to speak to at Telkom to actually find out what the problem is. The staff at Telkom Vincent are very rude to her. They just say buy a new one. Surely there must be a guarantee on this. Her Telkom number is ********** 118. Please assist