Did the place you went to not have security cameras? Most retail stores do. If so, why didn't they just review the tapes? I remember when a store thought I stole a purse from them, I simply told them I paid for it, gave them all of my information and walked out. I'm not going to sit around and be accused of something I didn't do. They are rent-a-cops not actual police officers. They can't legally detain you, unless they have a valid reason. Since they didn't see you shoplift or had someone else tell them you shoplifted, they had no reason.

I always worry this will happen to me, because it's not like you carry every receipt you ever get on your person. But good job on keeping your clothes looking brand new I guess. :)