Defy stove poor service to pensioners

My Mum bought a defy stove on the 25/09/2019 Ok furniture deliver the stove. She ask way the stove is not n a box..they said it was the stove on the floor.. The next day my mum phone ok furniture to tell them the stove door didnt close proper...she can't bake a cake..and inside the oven it look like the oven make same rust...after she used the stove on top it look like the silver turns to copper and start to rust...they sent people out to check..they replace the gatgets on the ovendoor and a new glass and rubbers that seal the door...but it look like the door is scew..if she try to bake something everything's coming out is flat..the rust inside the oven can have health problems...she report it how many times and nothing happen..the stove on top look like an old stove..she dont use any chemicals in or outside only sunlight liquids they sent her a sms that the job is done..how can defy treat pensioners like that..they save to buy something new..and thats what they get..maybe they think because they are old..they will not live long enough to use it... before they see all the faults on the stove...that is very bad service... and then they give a 3 year guarentee..meaning what..they are suppose to give her a new one because thats what she paid for and save for..