Why do you advertise aspects and then refuse to honour them?

I have been attempting to purchase a Television for my mother. I specifically chose a Wednesday as I am a pensioner and therefore am entitled to a 10% discount. As I live in Cape Town and my mother in Durban I was about to purchase the TV online, but was informed that the discount was only applicable in store. That makes no logical sense whatsoever. Game if you are not prepared to honour your promises why bother making them in the first place