Takealot False Advertising - Visa Promotion

Takealot sent out a promotion where you get a R200 coupon when paying with your VISA card. I purchased goods and received the voucher. When I tried to use it, it failed and now takealot claim that even though in the email it only stated that it was valid till end of August it has expired because they only had 13100 vouchers. If that was the case why did they still send me the voucher? There is also no mention of this in the email. This was simply a dishonest marketing tactic to get more people to spend money with them.