Very angry and disappointed customer

Very disappointed with Ryobi. Bought a lawnmower from Builders Bedworthpark store just over a year ago. Had to take the lawnmower back twice over a period of 3 months (it has a 2 year guarantee). The last time I had to wait for 3 weeks to get it back. I'm using it for the 3rd time since and again it's starting to give problems to switch on. I barely started with the lawn. I'd like to get a new lawnmower or a refund, since the people at the repair department clearly don't know what they're doing.