Poor Service

I bought a body shaper yesterday 01.03.15 , when I get home I realised I mistakenly took a small size instead of a medium. The following day 02.03.15 I drove back after work to return it for a correct size. To cut the story short they totally refused to assist me in any manner. I requested that since they are refusing to give me a correct size , they must please credit my account since I won't be able to fit in a smaller size. It seemed as if I was talking to a brick, no emotions no sympathy what so ever. I asked for a store manager and I was told he has left for the day. What astonished me the most is that they kept my item even though they didn't want to credit my account. Peter, is this allowed? Is this not *****? I hope you help me find solution, you are my last hope since I couldn't even speak with a Store Manager.