Ryobi Angle Grinder

I purchased a grinder earlier today so that my gardener can cut a few small tree branches. He had problems from the start with changing disk. We were not able to change the disks. I took it back to Builders Express. I was told that I forced the grinder, I used a framing and ripping disk for soft wood to cut the branches, was told this is also the reason that it broke. Askes to speak to a manager but they are in a meeting. The staff does not know what the meaning of customer service is. Spoke to three people and none of them knew what to do. In future I will rather pay more and go to a hardware store than going back to Builders.