Swim suit return

I purchased two swim suits from them, a bikini and full costume. This is an online paltfrom and was my first time buying from them. I was told delivery takes about 3 days, it took 3 weeks. When I finally received my goods I realised that they were small. I didn't even need to wear them cos I could tell by just holding them. I then packed them back in the dusty plastic, and called in plus emailed asking to pls exchange them. These were not cheap, I spent R600. And I'm told that there is nothing they can do. I did not wear the costumes and I'm going on vacation next week, so I need to now buy new swim suits and I don't know what's gna happen with these ones that I have at home. I was not even met halfway Atleast, all that was said is he can't help me. I don't know what this service is called, but byiog. Online is really not on as the customer service is on 0%. I could of easily went to the mall and purchased my swimsuits and received them same day, not three weeks of waiting for something that's all.

Maybe they ought to have a size guide on their website, because this is not on at all