we want a refund please

we purchased a mop from the homemark store for work purposes. it was not suitable, so we took it back, unopened, to get a refund. they said no, and the manager offered to come do a demo for us to show us how it works. He only arrived 2 days later, after we phoned a few times to find out where he was. he then proceeded to open our unused mop that we bought and did the demo. when the floor had dried, it had terrible streaks all over it. that was exactly what we were trying to avoid, we have mirror shine tiles that cant be washed with water, otherwise they have to be polished after washing. we dont have time to wash AND polish our floor. He then phoned his superior, who said that she could have made an exception for us, but since the mop had now been used, she cant help us. That is RIDICULOUS! he came into our store and opened our new mop and used it, he should have known better and brought a demo model with. She then said to me that there is nothing she can do for me. That is unacceptable service. The manager was VERY unprofessional and lacks knowledge of company procedures. We would like a refund please as this was not our fault. the manager needs more training.