Shelley underwear

I brought a pack of three Shelley underware and the pink one stained my skin and caused a rash. Also after one wash and was correctly the elastic has gone to almost nothing? Thay are now too big for me and don’t hold or sit well. What can be done about this? Thay were perfect before being hand washed. Then had little to no elastic and the pink one stained my legs and gave me a rash?!