False marketing

I am.extremely disappointed as I was given a voucher of R100 if.I bought.for R250 or.more.and had.to use.it by 31 March which I did and all was good. However, I.decided.to.return what I had bought and exchange it.for something else and when I did that they would not allow me to use the.voucher again so in effect I.got.given it only.for.it.to.be.taken away.and.customer services.were completely disinterested!