Faulty vacuum and shoddy repair service from Hirsch

I bought a samsung vacuum a year ago at Hirsch, I have taken the vacuum in for repairs 3 times for the same fault, the vacuum does not have enough power when it is switched on the first 2 times they replaced the motor, but the vacuum still does not work, I took it back a third time a day after collecting it from the second repair and now I am told that their is a maintenance problem and the filter needs to be replaced by me. There is still a year warranty left on the vacuum but it doesn’t seem like I will have a working machine before the warranty is over. I asked for a credit so I could get a different vacuum as there is clearly a problem with this one, but this has been declined. The vacuum has now been with Hirsch for a month. I am not sure what I need to do to get this vacuum replaced.