Withdraw offer

When I enquire about an Iphone and Ipad on 13/07/2015 the sales person offer a insurance deal and I told him I don't want it as I don't make decisions immediately. <br> After I got home I had some time to think about the deal.<br> On Sunday 19/07/2015 I visit the store again and ask them for the insurance and was told me the deal was only valid for the 13th when I have paid for the Iphone and Ipad.<br> I think this is bad practice to withdraw the offer and not telling me that was only valid for the day you buy it<br>