I purchased an ARGOS item online for my brother in UK and was then offered a discount on future purchases - which I accepted as I thought my brother could benefit if he wanted to make further purchases from his local ARGOS store.
A month later I found my Mastercard had been charged 10 pounds for "membership" of a company firstname.lastname@example.org
biller name: SHOPPERDISC.CO.UK
I wrote to ARGOS complaining - they accepted no responsibility whatsoever.
Still awaiting reply from SHOPPERDISC.CO.UK
You'll see from an online search that MANY others have has the same experience.
Laws need to change for customers to have any proper redress.