BUILDERS WAREHOUSE STAFF IDIOTS

I am realy upset with the way and maner I was treated and that I was denied a refund for a product that I bought at Builders in Rossburgh. I bought a sander, and after taking it home and sanding for less than 10 seconds I noticed that the sander slows down yo a point that it barely does any sanding. I was able to hold the sanding platform in place and still while the machine is at full speed. I packed it away and took it back to builders. They told me they cant take it back because its used.. Consumer return a t states that one can return anything within 7 days if its not satisfactory. After tryi g to explain to the manager that I had to use it inorder to notice that its not wotking to my liking, tbey kept telling me I cant return it since its been used. Ive sent emails to builders main office.. And to everyone I can try find to help me.. But they keep ignoring me.