Untrue adverti*****t!!!! Bad business style

We have been to the store middelburg mall on Saturday and saw the advert about your wonderfit promotion R50 for each used jean. This morning i took in 9 used jeans thinking i would buy with the vouchers a new pair of wonderfit jeans the lady attended to me told me for the first time there that it is 1x old jean for a R50 voucher per 1x new wonderfit product. No where there are any terms and conditions on the advert or on the voucher! This advert is very much confusing as we are to understand that they will give us a R50 voucher to use as we like not like they are saying 1x voucher per item.