Giving back broken goods and saying it's been fixed

My mum bought a reclining couch from OK furnitures in South gate mall and it is still under guarantee. The lever broke and she took it back so they could repair it after waiting for 1 month she phoned them yesterday (22/09/2017) asking if it has been repaired and they told her they will repair it asap and then phoned to tell her it has been repaired. So she fetched the couch and when she got home, it broke again. On further inspection she realized they just used a string to repair it. She phoned them once again and they told her to bring it again. I mean this costs petrol money,going up and down. Why can't they repair it properly in the first place. How can they have the audacity to use a string and say it's been repaired! If they can't repair the thing she should get a full refund because this is getting ridiculous now!