THE FABRIC IS "GREEN" - BUT WHAT"S WITH THE STRETCHING SCENE?

I purchased two pairs of RealBasics "recycled fabric" leggings (I think they were on a special) at Pick 'n Pay Clothing, Capricorn, on 15/10. I am a size 36 usually, but the items weren't labelled thus, so I chose a large-sized black and dark blue pair. When I tried the black pair on at home it fitted perfectly, but the waist stitching of the blue pair immediately started popping and it was clearly not the size marked. I returned these during the requisite one-month period, showed the shop assistant the clear size discrepancy and swapped them for another pair (large) that matched the waist size of the black pair that had fitted perfectly. However, on later actually wearing the black leggings (and subsequently the blue ones) to work for just one day each, they look like jodhpurs, with baggy elephant knees to boot! Although I have slender legs, I can assure you that I have not lost weight during one month, and that the new blue pair also fitted perfectly when I tried it on. I only discovered this last week (as I had had no occasion to wear either pair before.) I am now out of the guarantee period! I realise that they were inexpensive garments and that this sounds like a First World Problem, but if "recycled fabric" (whatever that means) stretches so much after just one day's wear, it doesn't seem to be ideal legging fabric. Furthermore, the CMT and sizing is shoddy. The cheap leggings I bought from the Chinese shop next door fitted perfectly and still look great, after months of wear! I wonder if others with my build have had the same problem with these particular "Green" leggings? I'm a bit disappointed with my purchase and cannot now return the items. Any comments?