Customer Service on returns pathetic

I went shopping with my mom for a swimsuit. The store in Three Rivers didn't have the right size but we purchased the next size up, willing to take it in a bit as we only had that day to find one. There are NO SIGNS that says you can't return swimwear, no one told us. The assistant asked if she had fit it and was happy, we said sure as we thought she was being polite. We then went to the Vaal Mall right after and found the right size, we wanted to return the other but was told we can't as it is printed on the BACK OF THE TILL SLIP! So you have to buy it first to find out you can't return it. The store told us to go back to the other Miladys because if they didn't tell us we can't return it, they have to refund us. We went back there and was again told NO! We can understand for hygienic reasons why, but this was within hours, straight from one store to the next??? Hygiene?! What guarantee can Miladys give ME that any swimsuit I purchase was NOT fitted by someone that was naked?? My mom now has TWO swimsuits, one she has used because it is her size, now she MUST keep the R400 bigger size simply because she took it out of the store?! This is ridiculous, there is no pre-warning in the shop, no one told us and it's printed on the back of a slip AFTER you buy it and seriously, who reads the back of their till slip right after paying? This means I can go into any Miladys, fit swimsuits to my hearts delight whilst naked, removing the hygiene sticker, hang them all back for the next person and that is ok, as long as I don't dare buy one and leave the store, then it's not hygienic? If we went home with it and came back the next day, different story, but we had the slips to show the time difference, that we went to the next store and back, still sealed and tagged. My mom will now keep the wrong size but Miladys will never see my money again.